THE  NUCLEATION 


OF  THE  UNCONTAMINATED  ATMOSPHERE 


BY  CARL  BARUS 
Hazard  Professor  of  Physics,  Brown  University 


WASHINGTON,  D.  C. : 

Published  by  the  Carnegie  Institution  of  Washington 
January,  1906. 


CARNEGIE   INSTITUTION   OF  WASHINGTON 
PUBLICATION  No.  40 


FROM   THE  PRESS  OF 

THE  HENRY  E.  WILKENS  PRINTING  CO. 
WASHINGTON.    D.    C. 


PREFACE. 

The  object  primarily  in  view  when  the  present  experiments  were 
begun  was  a  continuous  record  of  the  nucleation  of  the  atmosphere  in 
a  locality  relatively  free  from  the  habitations  of  man,  and  therefore  free 
from  nucleations  of  local  and  artificial  origin.  In  other  words,  it  was 
to  be  determined  whether  below  the  fog-limit  of  dust- free  air,  i.  e.,  below 
the  least  exhaustion  at  which  filtered  air  condenses  without  foreign 
nuclei,  the  atmosphere  contains  any  nucleation  whatever  beyond  that 
introduced  from  terrestrial  sources  and  coming  chiefly  from  the  origin- 
ally ionized  products  of  combustion.  An  investigation  of  this  kind 
seemed  well  worth  while,  after  it  had  been  shown1  that  the  nucleation  of 
the  atmosphere,  even  above  cities,  obeys  certain  clear-cut  laws,  showing 
a  marked  tendency  to  reach  an  enormously  developed  and  sharp  maxi- 
mum in  December  and  a  flat  but  very  low  minimum  in  June.  The 
former  at  least  does  not  in  general  coincide  with  the  period  of  maxi- 
mum cold,  and  the  possibility  that  some  effect  from  without  was  super- 
imposed on  the  local  effect  seemed  sufficiently  probable  to  warrant 
special  inquiry.  This  was  carried  out  as  detailed  in  Chapters  IV  and  V 
of  the  present  memoir,  in  two  series  of  observations,  made  with  similar 
apparatus,  simultaneously  at  Providence  and  at  Block  Island.  The  two 
stations,  lying  about  70  kilometers  apart,  pass  through  practically  the 
same  meteorological  variations  of  wind  and  weather;  while  Block 
Island,  surrounded  by  a  body  of  water  whose  smallest  radius  is  nearly 
20  kilometers  from  the  center  of  the  island,  while  one-half  of  it  fronts 
the  ocean,  is  in  the  winter  at  least  nearly  free  from  local  effect.  Leav- 
ing the  detailed  discussion  of  the  results  to  the  chapters  specified,  it  is 
noteworthy  that  the  average  monthly  nucleations  at  both  points  of 
observation  show  the  same  law  of  change,  though  the  actual  fluctuation 
at  Providence  is  naturally  less  salient.  The  data  found  at  each  station 
prove  that  the  tendency  to  pass  through  maxima  in  December,  observed 
at  Providence  in  1902-03  and  1903-04,  has  again  unmistakably  asserted 
itself.  In  addition  to  this,  however,  the  observations  at  both  stations 
developed  a  new  and  surprisingly  pronounced  maximum  in  February  as 
the  chief  feature  in  the  nucleations  of  the  last  winter.  Predominating 
in  each  of  the  series  of  results  over  the  earlier  maximum,  and  holding 

1  Barus  :  Smithsonian  Contributions,  Vol.  XXXIV,  1905. 


IV  PREFACE. 

for  different  bodies  of  air,  the  February  maximum  at  least  can  not  be 
of  local  origin ;  and  it  is  thus  in  a  measure  probable  that  the  December 
maximum  also  is  due  to  non-local  causes.  But  whether  these  are  the 
aggregated  effects  of  remote  terrestrial  sources,  or  whether  they  repre- 
sent an  actual  invasion  of  the  atmosphere  on  the  part  of  some  cosmic 
agency,  remains  to  be  seen. 

The  air  to  be  treated  in  the  present  series  of  experiments  is,  therefore, 
continually  approaching  a  state  of  purity  so  far  as  foreign  admixtures 
are  concerned.  Hence  the  properties  of  dust-free  air,  or  in  practice  of 
filtered  air,  became  increasingly  important.  It  may  be  proved  by  aid 
of  the  inclosed  steam- jet1  that  even  dust- free  air  must  be  an  aggregate 
of  nuclei,  whose  number  grows  rapidly  larger  as  their  diameter  de- 
creases, with  a  maximum  for  molecular  dimensions;  or  that  size  is 
distributed  among  the  molecules  and  quasi-molecules  of  dust-free  air 
in  a  way  somewhat  recalling  the  distribution  of  velocity  among  mole- 
cules, and  that  among  particles  larger  and  smaller  the  air  molecule 
represents  a  condition  of  maximum  occurrence.  The  fog-limit  of  dust- 
free  air  is  thus  a  variable  quantity,  depending  eventually  on  the  details 
of  the  method  of  nitration,  or  other  process  for  rendering  the  air  dust- 
free.  In  fact,  as  the  fog-limit  rises,  the  coronas  for  a  given  exhaustion 
above  the  fog-limit  increase  in  aperture,  up  to  a  limit.  It  should  always 
be  remembered  that  the  particles  or  nuclei  here  in  question  are  very 
small,  even  in  comparison  with  ions. 

With  the  object  of  meeting  the  state  of  things  in  question,  systemat- 
ically, the  data  in  Chapters  I,  II,  and  III  were  investigated,  while 
Chapter  VI  contains  a  summary  of  the  work  as  a  whole.  The  method 
employed  is  believed  to  be  a  new  departure,  inasmuch  as  all  results  are 
expressed  in  terms  of  the  number  of  nuclei  observed  per  cubic  centi- 
meter, so  that  the  nucleations  produced  are  the  criteria  throughout.  To 
offer  conditions  sufficiently  varied  for  the  experimental  work,  the  nucle- 
ation  of  dust-free  air  is  in  these  chapters  coarsened  by  ionizing  it,  either 
by  the  X-rays  or  by  a  weak  sample  of  radium  acting  through  a  sealed 
tube.  It  thus  appears  that  the  ions  or  fleeting  nuclei  resulting  are  also 
pronouncedly  of  all  sizes  within  limits  and  that  the  increment  of  nuclea- 
tion  between  two  definite  degrees  of  exhaustion  (i.  e.}  degrees  of  sudden 
cooling)  above  the  fog-limit  but  not  too  far  from  it,  is  greater  as  the 
radiation  applied  from  without  is  more  intense.  Virtually  the  grada- 
tion of  particles  is  thus  more  fine-grained  or  more  nearly  continuous 
with  the  efficient  nuclei  lying  within  closer  limits  of  size,  as  the  ioniza- 
tion  is  more  intense. 

:  Bulletin  U.  S.  Weather  Bureau,  No.  12,  1893. 


PREFACE.  V 

Throughout  the  whole  research  the  important  bearing  of  the  solu- 
tional  or  water  nucleus1  on  the  phenomena  of  condensation  is  manifest. 
If  the  nucleus  is  soluble  in  water,  vapor  pressure  decreases  with  the 
continued  evaporation  of  the  fog  particle,  until  the  decrement  of  vapor 
pressure  due  to  increased  concentration  of  the  solution  is  equal  to  the 
increment  due  to  increased  curvature.  The  result  is  a  persistent  solu- 
tional  nucleus  (water  nucleus),  necessarily  larger  than  the  original 
nucleus  of  solute.  A  great  variety  of  puzzling  phenomena  like  the  alter- 
nations of  efficient  nuclei  in  successive  otherwise  identical  exhaustions, 
the  persistence  of  fleeting  nuclei  or  ions  on  solution,  the  lowered  fog- 
limit  of  an  evaporated  corona,  etc.,  thus  find  a  satisfactory  explanation. 

The  final  general  result  to  be  referred  to  here  is  the  readiness  with 
which  nuclei  are  produced  by  the  gamma-rays,  even  after  penetrating  a 
centimeter  or  more  of  lead,  together  with  the  distinction  which  is  thus 
drawn,  experimentally,  between  these  rays  and  the  X-rays.  The  latter 
show  small  penetration,  but  are  so  phenomenally  active  in  producing 
secondary  radiation  that  to  a  wooden  fog-chamber  the  distance  effect 
for  a  radius  of  over  six  meters  between  bulb  and  fog-chamber  is 
relatively  neglible.  The  effect  of  the  gamma-rays,  on  the  contrary,  in 
spite  of  the  remarkable  penetration  evidenced,  for  instance,  by  the 
nucleation  produced,  is  nearly  vanishing  when  tested  by  the  same 
nucleation  at  a  distance  of  but  50  centimeters.  Again,  within  the 
fog-chamber  the  distribution  of  nuclei  along  the  axis  is  in  both  cases 
uniform  for  all  distances  (50  cm.)  within  the  range  of  observation, 
except  when  the  X-radiation  is  sufficiently  intense  to  produce  persist- 
ent nuclei.  In  this  case  the  curiously  pronounced  distribution  detailed  in 
Chapter  I  is  observed,  which  seems  to  show  either  that  the  nucleation 
originates  in  the  walls  of  the  vessel  or  that,  in  consequence  of  second- 
ary radiation,  the  density  of  ionization  near  the  walls  is  such  as  to 
promote  rapid  growth  of  nuclei  in  those  parts  to  abnormal  sizes.  The 
nuclei  in  question  are  over  200  times  more  persistent  than  the  ions,  and 
if  they  decay  by  breaking  into  like  fragments  one  may  estimate  that  the 
former  are  5  or  6  times  larger  in  diameter  than  the  latter.  Persistent 
nuclei  produced  by  the  X-rays  require,  in  fact,  but  a  vanishing  pres- 
sure difference  to  induce  condensation.  They  have,  moreover,  the 
property  of  increasing  in  number  if  left  without  interference  for  a 
short  time  after  radiation  ceases. 

In  view  of  the  interest  which  thus  attaches  to  dust-free  or  filtered  air, 
the  nuclear  systems  of  which  are  throughout  small  as  compared  with 

1  Barus  :  Structure  of  the  nucleus,  Smithsonian  Contributions,  No.  1373,  1903. 


VI  PREFACE. 

the  much  coarser  ions,  and  show  rapidly  increasing  numbers  with 
decreasing  size  until  the  molecular  dimensions  are  reached  or  even  sur- 
passed in  degrees  of  smallness,  I  have  undertaken  and  have  now  in 
progress,  under  the  auspices  of  the  Carnegie  Institution  of  Washington, 
a  systematic  research  on  the  properties  of  filtered  air.  The  fact  that 
the  nucleation  responds  to  very  penetrating  rays,  like  the  gamma-rays 
of  radium,  adds  additional  interest  to  the  inquiry. 

In  conclusion,  it  gives  me  pleasure  to  acknowledge  my  indebtedness 
to  Mr.  Robinson  Pierce,  jr.,  for  the  efficiency  and  patience  with  which 
he  conducted  the  measurements  of  nucleation  at  Block  Island,  placed 
in  his  charge  under  the  very  trying  mid- winter  conditions  there  encoun- 
tered. His  results  are  given  in  Chapter  IV.  I  am  further  indebted  to 
Miss  lyillie  L,.  Scholfield,  by  whose  skill  in  drawing  and  experience  in 
editorial  work  I  have  materially  profited. 

My  thanks  are  due  finally  to  the  Chief  of  the  U.  S.  Weather  Bureau, 
for  his  kindness  in  placing  suitable  quarters  for  observation  in  the 
Weather  Bureau  Building  at  Block  Island  at  our  disposal,  and  to  Mr. 
Day,  the  officer  in  charge  of  the  station,  for  many  courtesies  throughout 
the  work. 

CARI,  BARUS. 

BROWN  UNIVERSITY,  Providence,  R.  L,  July,  1905. 


CONTENTS. 


CHAPTER  I. — Results  with  an  Objective  Method  of  Showing  Distribu- 
tions of  Nuclei  Produced  by  the  X-rays  or  Other  Radiation. 

PAGE 

1.  Introductory    i 

2.  Apparatus    i 

3.  Vertical  radiation  at  one  end  of  the  trough,  entering  through  wood ....  2 

4.  Axial  radiation  entering  one  end  of  the  trough 3 

5.  The  same  continued  for  larger  pressure  differences 4 

6.  Condensation  of  dust-free  moist  air  in  the  absence  of  X-ray  nuclei. 

Fog  -limit  4 

7.  Possibility  of  producing  nuclei  by  sudden  intense  exhaustion 5 

8.  Successively  increasing  times  of  exposure  to  X-radiation 6 

9.  Symmetrically  graded  sizes  or  numbers  of  fog  particles 7 

10.  Possible  origin  of  nuclei  at  the  walls  of  the  receiver 9 

11.  Absorption  of  ions  at  the  walls  of  the  receiver 10 

12.  Summary    10 

13.  Tentative  experiments  with  lead  screens,  inside  and  outside  the  fog 

chamber    n 

14.  The  same  continued,  with  change  of  apparatus 13 

15.  Conclusion  16 

CHAPTER  II. — Numbers  and  Gradations  of  Size  of  the  Efficient  Nuclei  in 
Dust-Free  Air,  Energised  or  not  by  X-Ray  or  Other  Radiation. 

EXPERIMENTS  WITH  DUST-FREE  AIR  NOT  ADDITIONALLY  ENERGIZED. 

16.  Apparatus 17 

17.  Manipulation.    Fog  limit 18 

18.  Alternations  of  large  and  small  coronas  (periodicity) 18 

19.  Effect  of  lapse  of  time  on  the  nucleation  of  dust-free  air  imprisoned  in 

the  fog  chamber 21 

20.  Effect  of  pressure  difference  on  exhaustion 22 

21.  Remarks  on  the  tables 25 

22.  Blurred   coronas 27 

23.  Time  effect 27 

24.  Oscillations  at  variable  pressure  differences 27 

25.  Nucleations  at  varying  pressure  differences 27 

26.  Fog  limits 28 

27.  Oscillations  at  fixed  pressure  differences 29 

28.  Undersaturation  29 

29.  Undersaturation  continued 30 

30.  Nucleation   31 

EXPERIMENTS  WITH  DUST-FREE  AIR  ENERGIZED  BY  RADIUM. 

31.  Effect  of  radium  in  hermetically  sealed  glass  tube 32 

32.  Remarks  on  the  tables 35 

33.  Data  for  nucleation 36 

34.  Fog  limits  raised  by  weaker  ionization 37 

vii 


VIII  CONTENTS. 

PAGE 

35.  Nucleation   38 

36.  Radium  in  sealed  aluminum  tube 39 

EXPERIMENTS  WITH  DUST-FREE  AIR  ENERGIZED  BY  THE  X-RAYS. 

37.  Persistence  of  nuclei  due  to  X-rays  in  the  lapse  of  time 41 

38.  Fog  limits  for  nuclei  produced  by  X-rays 42 

39.  Sudden  exhaustion  in  the  absence  of  condensation 43 

40.  X-ray  nuclei  at  different  high  pressure  differences 45 

CHAPTER  III. — Critical  Conditions  in  the  Formation  of  Ions  and  of  Nuclei. 

41.  Apparatus.    X-ray  bulbs 47 

42.  Fog  chambers.    Filters  with  saturator 48 

43.  Notation  49 

EFFECT  OF  LARGE  PRESSURE  DIFFERENCES. 

44.  Nuclei  in  dust-free  air,  not  energized 49 

45.  Dust-free  air  energized  by  the  X-rays  from  a  distance 51 

46.  The  same  continued.    Rays  not  cut  off  during  condensation 53 

GENERATION  AND  DECAY  OF  NUCLEI. 

47.  Fleeting  nuclei 54 

48.  Persistent  nuclei 57 

49.  Persistence  of  fleeting  nuclei  after  solution 60 

50.  Enlargement  of  nuclei  in  dust-free  non-energized  air 62 

51.  Occurrence  of  water  nuclei 63 

52.  Cause  of  periodicity 64 

53.  Rain  64 

54.  Persistent  nuclei  in  general 65 

55.  Graduation  of  size  of  fleeting  nuclei.    Fog  limits 66 

56.  Secondary  generation 69 

NUCLEATION  DUE  TO  RAYS  PENETRATING  FROM  A  DISTANCE  OR  THROUGH  DENSE  MEDIA. 

57.  Effect  of  distance  of  the  X-ray  bulb  from  the  free  wooden  fog  chamber.  71 

58.  Generation  and  decay  for  radiation  from  D  =  200  cm 73 

59.  Electrical  effect  for  different  distances 75 

60.  Apparent  penetration  of  the  X-rays  coming  from  600  cm 75 

61.  Apparent  penetration  of  the  X-rays  coming  from  200  cm.  and  from 

6  to  7  cm 78 

62.  Generation  through  lead  plate  and  through  iron 79 

FOG  CHAMBERS   INCLOSED  IN   CASKETS. 

63.  Wood  fog  chamber  in  lead  casket    Penetration 80 

64.  The  same  continued.    Radiation  from  a  distance 81 

65.  Glass  fog  chamber.    Radiation  from  a  distance 84 

66.  Radiation  from  a  distance.    Glass  fog  chamber  in  lead  case. 84 


CONTENTS.  IX 

NUCLEATION  DUE  TO  GAMMA  RAYS. 

PAGE 

67.  Lead-cased  wood  fog  chamber.    Penetration ,  85 

68.  The  same  continued 85 

69.  The  same  continued.    Effect  of  distance 87 

70.  Glass  fog  chamber.    Penetration 88 

71.  The  same  continued.    Radiation  from  a  distance 89 

72.  Distribution  of  nucleation  along  the  axis,  within  the  fog  chamber 90 

73.  General  remarks 9° 

CHAPTER  IV.— -The  Nucleation  of  the  Atmosphere  at  Block  Island,  by 
Robinson  Pierce,  Jr. 

74.  Introductory 91 

75.  Apparatus 91 

76.  Observations 101 

77.  Remarks  on  the  tables.    Wood  fog  chamber 101 

78.  Continued.    Brass  fog  chamber 102 

79.  Summary  and  comparisons 103 

80.  Tentative   inferences  107 

81.  Average  daily  nucleations  at  Block  Island 109 

82.  Average  monthly  nucleations  at  Block  Island no 

CHAPTER  V.—The  Cotemporaneous  Nucleations  of  the  Atmosphere  at 
Providence  and  at  Block  Island. 

83.  Introductory IXI 

84.  Observations i" 

85.  Comparison  of  the  data  for  Providence  and  for  Block  Island 120 

86.  Average  daily  nucleations 127 

87.  Average  monthly  nucleations 128 

88.  Conclusion 130 

CHAPTER  VI.— Summary  and  Conclusions. 

89.  Introductory , 132 

90.  Notation 133 

91.  Fleeting  nuclei.     Ions J33 

92.  Fog  limits  of  fleeting  nuclei *34 

93.  Persistent  nuclei T35 

94.  Fleeting  nuclei  become  persistent  on  solution.    Origin  of  Rain 137 

95.  Solutional  enlargement  of  the  nuclei  of  dust-free  air i38 

96.  Water  nuclei.    Solutional  nuclei  in  general 14° 

97.  Alterations  of  large  and  small  coronas.  Periodic  distributions  of  effi- 

cient nuclei  in  dust-free  air i4r 

98.  Cause  of  periodicity 14* 

99.  Persistence  in  general *4r 

100.  Secondary   generation I41 

101.  Space  surrounding  the  X-ray  tube  a  plenum  of  radiations 142 

102.  Lead-cased  fog  chamber 143 

103.  Possibility  of  two  kinds  of  radiation  from  the  X-ray  tube 145 


X  CONTENTS. 

PAGE 

104.  Nucleation    due    to    gamma-rays 145 

105.  Distribution  of  nucleation  within  the  fog  chamber.    Radium 146 

106.  The  same  continued.     X-rays 146 

107.  Origin  of  persistent  X-ray  nuclei 147 

108.  Order  of  size  of  persistent  X-ray  nuclei 148 

109.  Ordinary  nuclei 149 

no.  Ordinary  dust- free  air  an  aggregate  of  nuclei 149 

in.  Nucleation  of  filtered  air 150 

112.  Nucleation  of  atmospheric  air  not  filtered.    Dust  contents  at  Provi- 

dence   151 

113.  The  same  continued.     Dust  contents  of  atmosphere  at  Providence 

and  Block  Island  compared 152 


LIST  OF  ILLUSTRATIONS. 


PAGE 

FIG.  i.         Fog  chamber  with  appurtenances  and  X-ray  bulb,  X 2 

2-6.      Diagram  of  a  succession  of  distorted  coronas 7 

7.         Computed   curves 8 

8-10.    Forms  of  lead  screens n 

1 1- 12.    Fog  chambers  with  screens  and  X-ray  bulb 14 

13.         Fog  chamber  with  axial  and  oblique  radiation 15 

14-18.  Graphs  showing  the  alternations  of  the  apertures  (,?)  of  corona 

in  non-energized  dust-free  air 21 

19.        Decay  of  the  nuclei  examined  in  the  lapse  of  hours 21 

20-25.  Change  of  apertures  ($)  of  coronas  and  number  of  efficient 
nuclei  («)  varying  with  the  different  pressure  differences  for 

the  cases  of  superior  and  inferior  coronas 26 

26.  Number  of  efficient  nuclei  («)  obtained  in  successive  exhaus- 
tions of  dust-free  air  energized  by  radium 34 

27-30.  Change  of  aperture  (j)  of  coronas  and  nucleations  («)  vary- 
ing with  the  pressure  differences  in  cases  of  dust-free  air 

energized  or  not  by  radium   (in  sealed  glass) 34 

31-32.  Decay  of  the  nuclei  produced  by  radium  after  the  removal  of 

the  tube  from  the  fog  chamber 34 

33.34.  Apertures  of  coronas  (j)  and  nucleations  (n)  varying  with  the 
pressure  differences,  for  the  case  of  dust-free  air  energized 

by  radium  acting  from  different  distances 36 

35-37-  Decay  curves  found  after  the  removal  of  the  radium  from  the 

fog  chamber 36 

38-39.  Apertures  (,y)  and  nucleations  (w)  varying  with  the  pressure 
differences  for  the  case  of  persistent  nuclei  produced  in  dust- 
free  air  by  the  X-rays 43 

40.  Filter  with  wet  sponge  tube  (saturator) 48 

41.  Rectangular  wood  fog  chamber 48 

42.  Cylindrical  glass  fog  chamber 48 

43.  Rectangular  fog  chamber 49 

.  44.        Cylindrical  fog  chamber 49 

45-51.  Illustrating  Tables  29,  32,  33,  34,  35,  36 51 

52-55.  Illustrating   Tables   30,   31     54 

56-62.  Illustrating  Tables   37,   38 62 

63-68.  Illustrating  Tables  39,  4O,  41 65 

69-78.  Illustrating  Tables  43,  44,  45,  49,  5<>,  53,  54 73 

79-82.  Illustrating  Table  47 76 

83-87.  Illustrating  Tables  47,  51,  53,  54 82 

88-90.  Illustrating  Table  56 88 

zi 


XII  LIST  OF  ILLUSTRATIONS. 

PAGE 

FIG.  91-92.    Graphs  showing  the  current  nucleations 104,  105 

93.  Chart  showing  the  average  daily  nucleations  at  Block  Island, 

in  hundreds  per  cubic  centimeter,  from  December  to  May, 
1904-05 106 

94.  Location  of  the  stations  at  Providence  and  at  Block  Island. .       106 
95-101.  Daily  record  of  the  nucleations  of  Providence  and  of  Block 

Island  in  thousands  of  nuclei  per  cubic  centimeter  from 
November,  1904,  to  May,  1905 120-125 

102.  Average  daily  nucleations  in  thousands  per  cubic  centimeter 

at  Providence  and  at  Block  Island  from  November,  1904,  to 
May,  1905 127 

103.  Average  monthly  nucleations  at   Providence   and   at  Block 

Island,  in  thousands  per  cubic  centimeter,  from  October, 
1902,  to  May,  1905 128 

104.  Average  monthly  nucleations  from  November,  1904  to  May, 

1905,  at  Providence  in  ten  thousands  per  cubic  centimeter, 
and  at  Block  Island  in  thousands  per  cubic  centimeter, 
showing  the  probable  run  of  the  curves  in  the  absence  of 
the  February  maximum  and  the  coincidence  of  the  maxima 
and  the  minima 129 


CHAPTER  I. 

RESULTS  WITH  AN  OBJECTIVE  METHOD  OF  SHOWING  DISTRIBU- 
TIONS OF  NUCLEI  PRODUCED  BY  X-RAYS,  FOR  INSTANCE.* 

1.  Introductory. — By  passing  the  X-rays  into  one  end  of  a  long  rec- 
tangular (virtually  tubular)  condensation  chamber  and  observing  the 
effect  produced  after  successive  different  intervals  ot  time  by  the 
condensation  method,  evidence,  with  a  possible  bearing  on  the  origin 
of  these  nuclei,  was  obtained.  The  coronas  are  distorted  and  at  first 
occur  on  the  bulb  side  of  the  apparatus  only.  The  distribution  of 
nuclei  is  inferred  from  the  form  of  the  corona. 

The  experiments  described  were  all  made  with  strictly  dust-free  air, 
as  both  the  method  of  precipitation  and  of  filtration  were  applied  prior 
to  each  experiment.  Furthermore,  as  the  exhaustions  necessitated 
the  use  of  short  lengths  of  rubber  tubing  (^,  ^,  and  i  inch  in  bore 
in  the  different  cases),  the  amount  of  sudden  cooling  obtained  does 
not  directly  correspond  with  the  pressure  difference,  8/>,  owing  to  the 
resistance  of  the  tube  to  the  flow  of  air.  The  data,  8p,  thus  refer  to  a 
given  type  of  apparatus,  but  they  are  satisfactory  as  relations,  so  long 
as  this  is  not  changed.  Furthermore,  the  pressure  difference  was  so 
adjusted  as  to  entrap  all  X-ray  nuclei,  to  the  exclusion  of  the  normal, 
quasi-molecular  nuclei  of  dust-free  air,  or  at  least  of  such  nuclei  for 
which  a  packed-cotton  filter  is  no  barrier. 

2.  Apparatus. — The  method  was  purposely  reduced  to  extreme 
simplicity,  and  the  apparatus  is  shown  in  figure  i.  A  B  is  the  long 
rectangular  condensation  chamber  of  wood  impregnated  with  resinous 
cement.  The  front  and  rear  faces  are  plate  glass,  through  which  the 
coronas  may  be  observed.  The  other  sides  are  lined  within  with  thick 
cotton  cloth,  kept  wet,  and  there  is  a  layer  of  water  at  the  bottom  to  in- 
sure complete  saturation  of  air.  C  is  a  stopcock  leading  to  an  efficient 
filter  (not  shown).  Supersaturation  is  produced  by  sudden  exhaustion 
at  the  B  end  of  the  apparatus,  while  the  A  end  receives  the  radiation 
from  the  X-ray  bulb,  X.  A  large  vacuum  chamber  was  placed  in 
connection  with  the  exhaust  pipe  shown,  through  a  wide  stopcock, 
the  details  of  which  need  not  be  explained.  The  X-rays  used  were 
not  very  penetrating,  and  were  obtained  from  a  soft  bulb  actuated  by 

*  Much  of  the  experimental  part  of  this  chapter  was  carried  out  by  Mr.  Robinson 
Pierce,  jr.,  and  myself,  conjointly. 


NUCLEATION   OF  THE  UNCONTAMINATED  ATMOSPHERE. 


a  small  induction  coil  (4"  spark)  and  3  to  5  storage  cells.  Two  filters 
of  solidly  packed  cotton  were  used,  one  7  inches  and  the  other  16 
inches  long.  They  were  about  equally  efficient. 


FIG.  i.— Fog  chamber,  AB,  with  appurtenances  and  X-ray  bulb,  X. 

3.  Vertical  radiation  at  one  end  of  the  trough,  entering  through 
WOOd. — In  the  preliminary  experiments  the  bulb  was  placed  so  as  to 
radiate  into  the  trough  in  the  position  shown  at  R,  and  kept  in  action 
5  minutes.  The  effect  was  then  observed  by  condensation  at  the 
pressure  difference,  8p=  17  cm.,  much  below  the  fog  limit  of  dust-free 
air  (section  6).  Two  results  were  noted  :  In  the  first  place,  while  the 
coronas  obtained  with  the  X-rays  in  bulky  apparatus  are  usually  of 
the  smaller  or  normal  type,  the  coronas  seen  in  this  shallow  apparatus 
were  often  enormous,  transcending  the  middle  green-blue-purple 
corona  (nucleation,  n=  100,000  per  cubic  centimeter).  Even  after  two 
or  three  subsequent  exhaustions,  filtered  air  being  added  prior  to  each, 
large  coronas  were  still  in  evidence.  In  the  second  place,  the  coronas, 
and  hence  the  nuclei,  were  observed  chiefly  on  the  A  side  of  the 
apparatus,  under  the  bulb.  Fearing  that  there  might  be  some  direct 
effect  due  to  induced  high  potentials,  the  X-ray  bulb  was  raised  10 
and  20  cm.  above  the  trough,  with  results  naturally  smaller  in  magni- 
tude, but  of  the  same  kind.  The  following  data  may  be  given: 

TABLET. — Number  of  nuclei,  n,  in  thousands  per  cm.3.     Sp  =17  cm.     Temperature 
about  20°.      Angular  aperture  <f>  =  5/30. 


Tim^  of  radiation 

Bulb  near  trough  (  2  cm.  )  . 

Bulb  10  cm. 
above  trough. 

Bulb  20  cm. 
above  trough. 

5  min. 

5  min. 

5  min. 

6  min. 

5  min. 

6  min. 

Coronas  on  — 
First  exhaustion  
Second  exhaustion  
Third  exhaustion  

S 

(*) 
5-9 

n 

68 

(*) 

n 

s 

(*) 
6-5 

5Q 

n 

JOO 

68 

• 

3-9 
2.7 

n 

20.5 
6.6 

8 

3-5 

2-7 

n 

15 
6.6 

• 
2.7 
1.9 

n 
6.6 

2.2 

*  Immense,  but  too  diffuse  for  measurement. 

In  all  cases  the  first  coronas  were  accompanied  by  dense  rain  and 
fogs,  frequently  in  horizontal  strata,  so  that  sharp  measurements  of 


UNILATERAL   RADIATION. 


aperture  are  generally  out  of  the  question.  Moreover,  the  first  con- 
densation is  accompanied  by  turbulent  displacement  of  fog  particles 
and  the  contents  of  the  receiver  are  thoroughly  stirred  up.  After 
filling  with  filtered  air  and  exhausting  again,  the  coronas  are  there- 
fore nearly  uniform  and  alike  on  both  sides.  In  the  above  table  the 
nucleation  produced  decreases  about  as  the  inverse  square  of  dis- 
tance, but  as  the  bulb  is  essentially  variable  in  intensity  such  a  result 
is  not  trustworthy. 

4.  Axial  radiation  entering  one  end  of  trough.—  Seeing  that  it  is 
possible  to  retain  the  nuclei  on  one  side  of  the  trough,  subsequent 
experiments  were  conducted  with  the  X-ray  bulb  placed  as  shown  at 
X  in  the  figure.  Moreover,  a  smaller  interval  of  radiation  was 
selected  to  more  and  more  fully  exclude  the  displacement  of  nuclei 
by  diffusion.  The  angular  diameters  (about  sj  30)  of  the  coronas  were 
measured  with  two  goniometers,  one  on  each  side  (A  and  B)  of  the 
trough,  the  distance  of  the  coronal  centers  from  the  bulb  being  about 
20  cm.  and  47  cm.,  respectively.  The  following  table  summarizes 
the  results  obtained,  remembering  that  all  initial  coronas  are  coarse 
and  blurred  and  accompanied  by  copious  rain  and  fog,  so  that  the 
diameters  must  be  estimated  : 


TABLE  2.  —  Number  of  nuclei  in  thousands  per  cm.3. 

diameter,  0  =  5/30. 


=  17  cm.;    angular 


Time  of  radiation. 

Corona  on  first 
exhaustion. 

Corona  on  second 
exhaustion. 

A  side. 

B  side. 

A  side. 

B  side. 

2  5  minutes 

5 

4-5 
4-5 
4.0 

2-5 

n 
32 
32 

22 

5-2 

5 

2.2 
2.2 
2.O 
0 

n 

3-3 

3-3 
2-5 
o 

s 

n 

5 

n 

3-2 

ii 

3-o 

9-3 

2      minutes  

2      minutes  

The  second  coronas  are  obtained  after  refilling  with  filtered  air,  and 
it  is  noteworthy  that  after  the  rains  of  the  foggy  first  coronas  fall  out 
(which  they  do  rapidly),  there  are  abundant  nuclei  left  for  the  next 
corona.  As  stated,  the  nuclei  are  now  uniformly  distributed  and  the 
coronas  persistent,  while  in  the  first  exhaustion,  apparently,  certain 
larger  particles  captured  all  the  moisture  and  removed  it  in  a  rainy 
precipitate.  The  smaller  particles  are  therefore  evaporated  into  water 
nuclei  (as  will  be  shown  below),  while  the  initial  temperature  of  the 
fog  chamber  is  being  rapidly  regained. 

It  is  to  be  observed,  moreover,  that  the  nucleations  on  the  A  and 
the  B  sides  in  these  cases  are  on  the  average  as  9 :  i ,  or  in  a  larger  ratio, 


4  NUCLEATION   OF  THE   UNCONTAMINATED  ATMOSPHERE. 

while  the  ratio  of  distances  is  below  1:2,  because  the  absorption  of 
the  wood  is  equivalent  to  a  removal  of  the  bulb ;  hence  the  density 
of  distribution  falls  off  faster  than  the  inverse  cube.  The  contrast  is 
even  greater,  because  in  the  2  or  3  minutes  of  radiation  some  nuclea- 
tion  must  arrive  on  the  B  side  by  convection  and  diffusion. 

We  were  originally  of  the  opinion  that  there  is  marked  absorption 
of  the  nucleating  power  of  X-rays,  by  the  successive  vertical  layers 
of  air  from  left  to  right,  but  it  is  best  not  to  prejudge  the  case  here. 

5.  Continued  for  larger  pressure  differences. — Several  questions  now 
present  themselves  for  immediate  decision,  viz,  whether  all  the  X-ray 
nuclei  have  been  caught  and  in  how  far  the  exhaustions  are  below 
the  point  of  spontaneous  condensation  of  moist  air.  Accordingly 
larger  pressure  differences  were  applied.  Table  3  gives  a  few  examples. 

TABLE  3. — Nucleations,  n,  in  thousands  per  cm.3.    Time  of  exposure  to  X-rays,  3.5 
minutes.     Angular  aperture  0  =  5/30. 


Side  A  B  A  B  A  B 

5=  4.6  1.8  3-9  2.1  2.8  2-5 

icr*n=  35  i.  9  27  3-5  "  7-8 

Ratio  18:1  7.7  :  i  1.4:1 

Hence  above  8p  =  2i  cm.  for  this  apparatus,  nuclei  show  themselves 
on  both  sides,  and  the  question  arises  to  what  extent  the  normal  air 
nuclei  (of  dust-free  air)  have  been  captured.  At  8/>  =  31  cm.  the  fog 
particles  condensed  on  X-ray  nuclei  probably  drop  out  at  once  and 
the  persistent  corona  observed  is  precipitated  on  the  normal  air  nuclei 
stated.  At  all  events,  the  gradual  evanescence  of  the  X-ray  effect  as 
8p  increases  is  noteworthy. 

6.  Condensation  dust-free  of  moist  air  in  the  absence  of  X-ray  nuclei  — 
Fog  limit.  —  With  the  object  of  finding  the  pressure  difference  of 
exhaustion,  8/>,  corresponding  to  the  lower  limit  of  spontaneous 
condensation  of  moist  air  without  foreign  nuclei,  experiments  were 
first  tried  with  a  cock  %  inch  in  bore,  in  the  exhaustion  tube.  The 
results  were  identical  on  the  A  and  the  B  sides,  as  follows  : 

TABLE  4.  —  Spontaneous  condensation  in  saturated  air.     Angular  aperture  <f>  =  sf$o. 

5p=  24cm  3icm 

5  =  2.2  2.7 

Repeated,  5  =  2.4  3.2 

s  =  2.1 

Do.,  large  filter,  s  —  2.2  3.5 

Do.  5  =  1.9 

Air  over  night,     s  =•  2.0 


22cm,  n  =  o 


FOG   LIMIT.  5 

This  indicates  that  at  a  pressure  difference  of  about  8/>0  =  22  cm.  for 
the  given  apparatus  and  dust-free  moist  air,  spontaneous  condensation 
with  vanishing  coronas  begins  on  sudden  cooling  and  that  thereafter 
the  coronas  increase  regularly.  This  pressure,  8/>0,  will  be  usually 
referred  to  as  the  "  fog  limit." 

In  corroboration  with  the  preceding,  similar  experiments  were  tried 
with  an  instantaneous  valve,  opened  with  a  hammer,  and  having  a 
clear  bore  of  over  i  inch.  The  results  shown  in  table  5  were  identical 
on  both  sides,  but  unexpectedly  irregular,  the  only  explanation  for 
which  might  seem  attributable  to  a  possibly  unequal  degree  of  sudden- 
ness in  opening  the  valve.  But  this  is  not  the  case;  for  alternations  of 
large  and  small  coronas  in  dust-free  air,  such  as  are  here  imperfectly 
shown,  may  be  kept  up  indefinitely  if  strictly  identical  conditions 
are  retained.  Effectively,  the  large  fog  particles  emit  more  nuclei,  the 
smaller  fewer  nuclei  for  the  next  condensation  in  order,  everything 
else  remaining  the  same.  The  importance  of  these  oscillations  about 
the  mean  aperture,  whether  the  emission  is  ionized  or  not,  can  not  be 
called  in  question,  as  I  shall  show  in  Chapter  II. 

TABLE  5. — Spontaneous  condensation  of  saturated  air.     Angular  diameter  0  =  5/30. 

Press,  diff.,  8p=  igcm  19.4™  2i.4cm  24cm 

s=  2.3  3.4  3.3  4.4 

Repeated,         5=  o  2.1  2.0  2.5 

s=  o  o  3.0  4.3 

5=  o  o  2.0  3.5 

^=  o  3.5  3.3 

5=  —  —  2.2  3-3 

ean<  (    n  =  o  o  7,600  21,000 

8^0<20cm,  n  —  o 

For  8^  —  19.4  an<i  below,  therefore,  no  nuclei  appeared  after  thor- 
ough cleaning.  For  &p  =  2o  cm.  and  above,  i.  £.,  at  a  somewhat 
lower  pressure  difference  than  before  in  consequence  of  more  rapid 
exhaustion,  spontaneous  condensation  begins.  The  large  coronas 
are  blurred.  Hence  in  neither  case  will  air  nuclei  be  caught  at 
Bp  —  17  cm.,  in  the  given  apparatus. 

f.  Possibility  of  producing  nuclei  by  sudden  intense  exhaustion.* — The 

condensation  of  the  moist  air  in  the  absence  of  foreign  nuclei  may 
be  considered  as  due  to  the  spontaneous  nucleation  of  the  air,  the 
available  nuclei  increasing  in  abundance  as  with  increasing  pressure 

*  Investigations  on  the  spontaneous  condensation  of  moist  air  were  first  suggested 
by  myself,  in  Bull.  U.  S.  Weather  Bureau,  No.  12,  1893,  pp.  13  and  48.  They  have 
since  been  fully  treated  in  the  masterly  work  of  C.  T.  R.  Wilson,  Trans.  Royal  Soc. 
Lond.,  vol.  189,  pp.  265,  307,  1897  I  ibid.,  vol.  192,  pp.  403-453,  1899. 


6  NUCLEATION   OF  THE   UNCONTAMINATED   ATMOSPHERE. 

differences  the  sizes  of  captured  nuclei  are  smaller,  until  the  air  mole- 
cule itself  is  approached.  It  follows,  then,  that  normal  dust-free  air 
always  contains  unstable  systems. 

Hence  the  question  may  well  be  asked  whether  very  sudden  and 
intense  exhaustion  may  not  itself  possibly  be  productive  of  nuclei. 
Thus,  if  an  unstable  molecular  configuration  is  just  about  to  break 
down,  it  is  conceivable  that  the  tendency  to  break  down  is  accentu- 
ated by  the  violent  treatment  in  question. 

We  made  some  experiments  on  this  subject,  by  looking  for  the 
presence  of  ionization  under  these  conditions,  using  a  pressure  differ- 
ence, S/>30  cm.,  by  placing  a  gold-leaf  electrometer,  properly  insu- 
lated, in  the  condensation  chamber.  The  loss  of  charge  in  damp  air 
is  at  first  surprisingly  small ;  nevertheless  the  experiments  are  very 
difficult  and  we  were  unable  to  come  to  a  conclusion. 

8.  Successively  increasing  times  of  exposure  to  X-radiation.— After 
this  digression,  experiments  were  resumed  with  the  apparatus,  as 
shown  in  figure  i.  The  pressure  difference,  8p  =  ij  cm.,  was  used 
throughout,  as  this  is  well  within  the  lower  limit  of  spontaneous  con- 
densation for  the  given  receiver,  while  coronas  may  be  obtained  with 
X-ray  nuclei  for  pressure  differences  even  lower  than  8fi=io  cm. 
Such  coronas  are  vague,  however,  until  the  rain  nuclei  are  thrown 
out,  and  on  second  exhaustion  (n  =  39,000,  5  =  4.8  were  usual  values 
after  4  minutes  of  exposure  to  the  radiation)  they  are  naturally  faint. 

The  immediate  incentive  to  the  work  of  the  present  section  was 
given  by  the  occurrence  of  elliptic  distortions  of  coronas,  as  shown 
in  the  following  tables : 

TABLE  6. — Distorted  coronas,  Increasing  times  of  exposure  to  X-rays.  8p  =  ij  cm. 
Coronal  center  19  cm.  (A  side)  and  46  cm.  (B  side)  from  bulb.  Angular  aperture 
0  =  -5/30. 

Time,  2  min. 


Side,  A  B 

First  exhaustion,      5  =  4.5,  elliptic,  strong.  i.o?   faint,  circular. 

Second  exhaustion,  5  =  2.7,  circular.  2.4      circular. 

First  exhaustion,       5  =  4.6,  elliptic,  strong.  o.o 

First  exhaustion,      s  =  4 . 6,  elliptic,  strong.  o.o 

TABLE  7. — Preceding  table  continued. 
Time,  i  min.  2  min.  3  min. 


Side,  ABA  B  A  B 

5=       3.1,  round,  o  4.1,  elliptic,  o  5.8,  ellipse,  larger  o 

strong.  strong.  and  distorted. 

On  second  exhaustion,  after  refilling  with  filtered  air,  the  coronas 
were  nearly  identical  on  both  sides. 


CAMPANULATE   CORONAS.  7 

A  series  of  observations  was  now  systematically  carried  out,  un- 
fortunately with  somewhat  weaker  radiation.  After  1,2,  and  3  minutes 
of  exposure,  respectively,  the  coronas  on  the  A  side  were  round  to 
roundish  (cf.  figs.  2  and  3),  of  gradually  increasing  strength  and 
density,  and  with  rainy  precipitation  and  fog  usually  marked.  There 
was  nothing  on  the  B  side  even  after  6  minutes  of  exposure.  After 
4  minutes  (cf.  fig.  4),  the  corona  became  spindle-shaped,  ^—5.4  cm. 
in  major  axis,  accompanied  by  rain  from  horizontal  layers  of  fog. 


5 
FIGS.  2-6. — A  succession  of  distorted  coronas. 

After  6  minutes  of  exposure  to  the  X-rays,  the  coronas  underwent 
remarkable  distortion,  becoming  gourd-shaped  (fig.  5),  often  with  a 
long,  serpentine  neck  dipping  into  the  B  side  of  the  condensation 
chamber.  The  length  of  figure  on  the  goniometer  was  about  6.8  cm., 
the  outline  being  orange  and  the  field  within  greenish.  Rain  and  fog 
abounded.  The  coronas  on  second  exhaustion  (after  adding  filtered 
air)  were  green-blue-purple,  5  —  4.9,  n  —  42,000,  and  white-red-green, 
5  =  4.5,  n  —  32,000,  on  the  A  and  B  sides,  respectively.  The  experi- 
ment was  repeated,  with  like  results. 

After  8  and  1 1  minutes  of  exposure,  both  the  A  and  the  B  sides 
became  the  seat  of  the  now  wedge-shaped  corona  (cf.  fig.  6),  greenish 
within  and  orange  in  outline.  There  was  much  rain  and  fog. 

Figures  2-6  are  seen  immediately  after  the  exhaustion.  A  moment 
later  there  is  a  storm-like  disturbance  in  the  condensation  chamber, 
accompanied  by  rain  and  fog.  Hence  the  distribution  of  nuclei  found 
on  exhaustion  is  incompatible  with  a  persistent  distribution  of  fog 
particles.  In  fact,  the  first  coronas  usually  fall  out  rapidly,  showing 
the  occurrence  chiefly  of  large  fog  particles  in  spite  of  the  corona. 
The  second  coronas  are  circular  and  persistent,  whence  a  nearly  uni- 
form distribution  of  nuclei  may  be  inferred. 

9.  Symmetrically  graded  sizes  or  numbers  of  fog  particles. — Since 
the  coronas  obtained  all  show  an  unmistakable  tendency  to  horizontal 
symmetry  with  reference  to  the  longitudinal  axis  of  the  condensation 
chamber,  the  nuclei  to  which  the  coronas  are  due  must  either  origi- 
nate in,  or  else  be  absorbed  by,  the  top  and  bottom  of  the  apparatus. 
Nuclei  originating  or  lost  at  the  front  and  rear  faces  are  nearly 
uniformly  distributed  normal  to  the  line  of  sight  and  produce  circular 


8  NUCLEATION   OF  THE   UNCONTAMINATED   ATMOSPHERE. 

coronas.  Nuclei  originating  or  lost  at  the  left-hand  end  of  the  cham- 
ber will  additionally  distort  the  corona,  and  such  distortion  is  clearly 
in  evidence,  apart  from  the  one-sided  position  of  the  coronas. 

Mere  inspection  of  the  coronas  (figs.  2-6)  shows  that  they  are  larger 
for  fog  particles  near  the  axis,  and  smaller  for  particles  near  the  top 
and  bottom  of  the  condensation  chamber.  Hence  it  is  next  necessary 
to  explain  that  the  details  of  the  distorted  coronas  observed  actually 
correspond  with  a  gradation  of  the  number  of  effective  or  available 
nuclei,  from  the  axis  outward  on  all  sides.  In  the  case  of  linearly 
graded  fog  particles  increasing  in  diameter,  8,  from  bottom  to  top,  it 
appears  that  the  equation  of  the  apertures,  s,  of  the  loci*  of  like  color 
of  the  corona  is 


s  =  —  r-^zr^z  (I~ \i  + 


a   sin   <£   V          X1  80 

where  s0  is  the  aperture  for  the  particles  of  diameter,  80,  in  the  horizon 
or  plane  of  sight,  and  8  the  angle  in  polar  coordinates  between  the 
radius  vector  to  the  part  of  the  corona  in  question  and  the  horizon- 
tal, the  origin  being  at  the  center  of  the  corona.  Finally  8  =  80— ah. 
Such  coronas  when  the  gradation  becomes  marked  are  campanulate 
in  outline,  finally  becoming  basin-shaped. 


FIG.  7. — Computed  curves. 

In  the  present  case,  however,  there  are  two  symmetrical  distribu- 
tions of  this  kind,  i.e.,  increasing  diameters  of  fog  particles  from 
the  axis  of  the  chamber  toward  the  top  and  the  bottom.  Hence 
pairs  of  intersecting  curves,  two  examples  of  which  are  given  in 
figure  7  (a!  >  a),  show  the  coronas  to  be  anticipated,  if  the  remote 
parts  beyond  b  and  c  of  the  corona  are  ignored  and  only  the  stronger 
curves  surrounding  the  spot  of  light,  d,  admitted.  In  other  words, 

*Barus:  Am.  Journ.  Sci.  (4),  XIII,  p.  309,  1902. 


SOURCES  OF  NUCLEI.  9 

as  the  distance,  b  c,  varying  with  the  number  of  axial  nuclei  and  the 
distribution  constant,  a,  increases,  all  the  figures,  2,  3,  4,  5,  6,  may  be 
logically  evolved. 

On  the  left-end  face,  moreover,  there  would  be  special  interference 
with  the  distribution  of  nuclei  giving  rise  to  the  corresponding  dis- 
tortion seen  in  the  coronas.  Further  distortion  due  to  the  decrease 
from  left  to  right  of  the  intensity  of  the  radiation  must  also  be 
apparent,  and  the  gradient  of  distribution  will  be  slightly  altered  by 
diffusion.  One  may  note  that  if  anything  issues  from  the  walls  of 
the  vessel,  it  comes  as  abundantly  out  of  the  water  below  as  out  of 
the  wet  cloth  above. 

10.  Possible  origin  of  nuclei  at  walls  of  receiver. — As  has  already 
been  suggested,  the  observed  gradation  of  fog  particles  may  result 
from  the  (real  or  virtual)  evolution  of  effective  nuclei  at  the  top  and 
the  bottom  of  the  apparatus,  in  consequence  of  the  impact  of  X-rays 
on  those  parts.  There  is  much  electric  evidence  against  such  an 
explanation  ;  nevertheless  it  is  worth  a  brief  examination,  particularly 
as  it  includes  the  effect  of  secondary  radiation  to  be  discussed  below 
(Chapter  III). 

The  enormous  coronas  which  have  been  obtained  with  the  above 
(shallow)  apparatus,  as  compared  with  the  small  coronas  seen  in  the 
cases  of  more  bulky  apparatus,  is  in  keeping  with  this  view.  Again, 
the  rapid  decrease  of  the  nucleating  power  of  the  X-rays  might  to 
some  extent  be  associated  with  the  increasing  obliquity  of  the  rays, 
but  no  evidence  of  this  was  found. 

The  observed  distortion  of  coronas  is  clearly  due  to  a  gradation  of 
nuclei,  either  as  to  size  or  number,  or  both.  If  efficient  nuclei  issue 
from  the  top  and  bottom,  they  must  be  present  in  greatest  number  near 
those  parts  of  the  apparatus,  and  consequently  the  largest  diameter  of 
coronas  should  apparently  be  found  there.  But  if  the  largest  number 
of  effective  nuclei  is  present  near  the  top  and  bottom,  the  tendency 
to  growth  by  cohesion  will  also  be  most  marked  in  those  regions. 
Hence,  with  this  admission,  the  largest  nuclei  must  be  looked  for 
nearest  the  top  and  bottom,  while  the  gradation  in  size  decreases  regu- 
larly toward  the  axis.  The  large  nuclei,  therefore,  may  be  sufficiently 
numerous  near  the  walls  to  capture  all  the  available  moisture  on  con- 
densation ,  leaving  the  small  nuclei  without  a  load  of  water  and  unable 
to  appreciably  descend.  Hence  the  marked  rain  effect,  the  rapidity 
with  which  the  first  coronas  usually  drop  out,  the  turbulent  motion 
which  succeeds  condensation,  the  occurrence  of  large  persistent  coronas 


10        NUCLEATION   OF  THE   UNCONTAMINATED   ATMOSPHERE. 

on  second  exhaustion  even  after  the  first  coronas  have  quite  dropped 
out,  etc.,  are  all  in  a  measure  accounted  for. 

Finally,  one  may  note  that  secondary  radiation  (the  importance  of 
which  I  at  first  underestimated)  issuing  from  the  top  and  the  bottom 
of  the  condensation  chamber  would  accentuate  the  present  effect,  or 
even  wholly  replace  it. 

Thus  it  seems  not  unreasonable  to  infer  that  nuclei  are  produced  by 
the  impinging  X-rays  in  much  the  same  way  in  which  they  are  pro- 
duced by  high  temperature  (ignition),  or  by  high  potential;  and  the 
question  arises  whether  the  nuclei  thus  put  in  evidence  may  not  be 
associated  with  the  electrons  to  which  the  cohesions  between  the 
molecules  may  be  ascribed. 

11.  Absorption  of  ions  at  walls  of  receiver.— if  the  nuclei  due  to  the 
ionization  of  air  by  the  X-rays  are  absorbed  at  the  walls  of  the  receiver  * 
a  diffusion  gradient  will  be  established,  resulting  in  a  decreasing  num- 
ber of  nuclei  from  the  axis  outward,  a  distribution  the  reverse  of  the 
preceding.      The  observed  distortion  will  therefore  here  be  due  to  a 
gradation  in  the  numbers  of  nuclei. 

One  difficulty  in  the  present  instance  seems  at  first  sight  to  be  fatal; 
for  no  reason  is  suggested  why  the  coronas  on  second  and  third 
exhaustion  do  not  eventually  show  flower-like  distortion ,  which  they 
never  do.  In  other  words,  it  is  here  tacitly  assumed  that  only  the 
nuclei  in  the  nascent  state,  as  it  were,  are  appreciably: diffusible,  while 
the  nucleus  is  relatively  a  fixture.  It  will  be  shown  in  Chapter  III, 
however,  that  on  second  and  third  exhaustion  all  the  nuclei  have 
probably  been  converted  into  solution al  water  nuclei  by  evaporation, 
so  that  the  difficulty  in  question  is  not  serious. 

12.  Summary. — To  decide  between  these  hypotheses  it  is  necessary 
to  guide  the  X-rays  by  screens,  suitably  placed  both  on  the  inside  and 
the  outside  of  the  apparatus;  but  these  experiments  will,  in  the  suc- 
ceeding chapters,  lead  to  results  much  too  diffuse  and  complicated  in 
character  to  be  summarized  at  present. 

Here  there  is  room  only  for  a  final  remark.  Whenever  nucleation 
and  ionization  are  associated  as  the  outcome  of  any  process  (physical 
or  chemical),  the  former  is  generated  proportionally  to  the  latter,  in 
such  a  way  that  each  is  produced  at  its  own  rate  depending  on  inci- 

*A  number  of  similar  cases  have  been  worked  out  in  Smithsonian  Contributions, 
No.  1309,  1901,  "Experiments  with  ionized  air;"  and  ibid.,  No.  1373,  Chapter  V,  1903. 


EFFECT  OF  SCREENS. 


II 


dental  conditions.  This  is  best  worked  out  with  water  nuclei.  The 
subsequent  life-history  of  the  nucleation  and  the  ionization  is  distinct, 
nuclei,  when  produced  by  intense  radiation  as  above,  being  surprisingly 
persistent,  ions  by  contrast  characteristically  fleeting.  Hence  it  seems 
to  me  to  be  best  in  keeping  with  all  the  data  in  hand  to  regard  the 
nucleation  as  the  product  which  owes  its  growth  or  origin  to  the 
expulsion  of  the  corpuscles  representing  the  concomitant  ionization. 
Ignition  and  high  potential  nuclei,  X-ray  and  radiation  nuclei  in 
general,  phosphorus  and  water  nuclei,  produced  throughout  in  strictly 
dust-free  air,  all  admit  of  this  account  of  their  occurrence  and  prop- 
erties. There  is  no  observable  case  of  a  process  producing  ionization 
without  nucleation,  although  there  are  many  cases  of  nucleation  free 
from  ionization. 

13.  Tentative  experiments  with  lead  screens,  inside  and  outside  of  the 
fog:  Chamber. — These  experiments  were  made  in  large  number;  but 
owing  to  the  variability  of  the  X-ray  bulb  and  the  action  of  the  coil, 
as  well  as  the  difficulty  of  realizing  truly  geometric  conditions  with 
X-radiation,  they  are  not  satisfactorily  conclusive.  It  will  be  seen  in 
the  following  chapters  that  results  like  the  present  can  not  in  any  case 
be  more  than  preliminary  in  character. 

The  screens  were  lead  plates  with  holes  cut  in  them,  or  lead  tubes 
soldered  to  the  edges  of  the  holes  normal  to  the  plate.  They  were 
placed  between  the  X-ray  bulb  and  the  A  end  of  the  fog  chamber  to 
guide  the  radiation. 


8 


FIGS.  8-10. — Forms  of  lead  screens. 

In  case  of  the  observations  i  to  6,  the  screen  was  in  the  shape  of 
figure  8,  with  a  horizontal  slit  10  cm.  long  and  1.5  cm.  wide,  stretching 
nearly  across  the  end  of  the  fog  chamber.  Often  screens  of  this  kind 
were  adjusted  2  to  3  cm.  apart,  as  shown  in  figure  9.  The  screen  was 
earthed  and  the  bulb  placed  as  near  it  as  practicable. 


12         NUCLEATION   OF  THE  UNCONTAMINATED   ATMOSPHERE. 


TABLE  8. — Miscellaneous  experiments,  chiefly  with  screens.  Long  fog  chamber,  vol. 
13,000  cm.3.  Sp  usually  17-18  cm.  Coil  with  4  cells.  Observations  at  middle  of 
chamber,  29  cm.  from  end. 


No. 

1 
2 
3 
4 
5 
6 

Expo- 
sure. 

Corona. 

s. 

Screen. 

Remarks. 

Min. 
10 
5 
11 
10 
7 
10 

Lead,  with  slit  
do  

Corona  strong;  clear. 
Corona  very  small. 
Corona  not  sharp. 
No  corona. 

do  

OvaP 

3.6 
0.0 
4.0 
3.0 

do 

Same  doubled  

Oval 

Screen  removed  
Double-si  itted  screen.  . 

Round  

7 

8 
9 
10 

11 

12 
13 
14 

15 

16 
17 

18 
19 

20 
21 

22 

23 
24 
25 

26 
27 

28 
29 
30 
31 
32 

33 
34 

14 

7 
12 
11 

11 

14 
13 

10 

20 

11 
11 

10 
10 

10 

11 

3 

5 
5 
5 

5 
3 

0.0 

6.1 
0.0 
0.0 

0.0 

0.0 
(?) 
5.0 

4.0 

3.0 
3.0 

0.0 
(?) 

(?) 
(?) 
Its,*  with  more  po 

A  side  full  

Lead,  with  tube,  2-5  cm. 
diameter,  8  cm.  long. 
Screen  removed  

On  both  A  and  B  sides. 
Corona  just  visible. 

Just   visible;    forms 
gradually. 

Small  corona. 
Large  diffuse  corona; 
strata. 
Strong  corona;  larger 
in  middle  of  appara- 
tus. 
Clear  corona  ;  little  fog. 
Clear  corona,  oval  on 
A  side. 
Coil  works  badly. 
Coil  works  badly  (?). 
Corona  just  appears. 
Small  coronas  thro  ugh- 
out  chamber. 

=  16.7. 

Second  corona  — 
52  =  3-4. 

*2  =  4.2. 
«2  =  large. 
*2=l-9. 

*2=1-1. 

{*1  =  2'.6! 
Corona  on  both  sides. 

Corona   horseshoe- 
shaped. 

Coil  improved. 

Oval 

Lead,  with  tube  (axial) 
Do.,  tube  directed  to 
bottom. 
Tube  axial 

Do.,  bulb  plate  normal. 
Tube  directed  to  glass. 

Clear.  

Oval 

Lead,  with  tube,  3.5cm. 
diameter,  4  cm.  long. 

do              ... 

do  
do  

do  

do 

do  

do 

do  
Recent  resu 

Distorted  ;  fog 
and  streamers. 
Campanulate  .  . 
Streamers  

do 

tverful  coil  (6  cells)  §p  = 

Disk  of  lead  3  cm.  in 
diameter  over  center. 
.....do  
do  
Hole  (2.  5  cm.)  in  lead 
plate. 
do  

do  
do  
3.6 

2.4 
A  and  B  sides  full. 
18.5 
6.4 
2.5 
4.5 
3.5 
1.6 

3.0 
3.5 

do  
Streamersf  
5j>  = 

Six  cells  

Lead  tube  at  top  

Roundish  

Open  on  top.... 

Roundish  
do  

Lead  tube  at  bottom.  .  . 

Lead  tube  axial  
do 

'•  All  lead  screens  earthed. 


t  Campanulate  on  B  side. 


Since  the  front  and  rear  faces  of  the  fog  chamber  can  only  contrib- 
ute a  distribution  of  nuclei  corresponding  to  round  coronas  with  the 
given  line  of  sight,  while  the  lead  cuts  off  most  of  the  efficient  radia- 
tion from  the  top  and  bottom,  round  coronas  should  appear  if  the 
nuclei  come  out  of  the  walls.  This  was,  in  fact,  the  case  in  the  first 
and  second  experiments,  where  clear,  round,  strong  coronas  were  ob- 
served; the  third  observation,  however,  leaves  the  question  in  doubt. 


EFFECT  OF  SCREENS.  13 

Similarly  conflicting  results  were  obtained  with  the  screen  (fig.  9), 
the  radiation  being  weaker  in  view  of  the  greater  distance  of  the  bulb 
from  the  fog  chamber  and  the  more  efficient  screening.  With  the 
lead  plates  removed,  the  usual  phenomena  (oval  coronas)  appear;  but 
throughout,  the  contrast  is  not  sharp  enough  for  definite  decision. 

Long  lead  screens  placed  horizontally  within  the  fog  chamber  oppo- 
site the  slit  in  the  external  screen,  as  at  A  in  figure  n,  did  not  stop 
the  radiation.  Elliptic  coronas  were  observed  around  the  trace  of 
the  screen  as  a  minor  axis,  precisely  as  if  the  internal  screen  were 
absent.  Hence  either  diffusion  or  secondary  radiation  must  be  very 
active  throughout  the  exposure. 

In  experiments  7  to  21  the  lead  screen,  figure  10,  was  a  broad  flange 
on  a  lead  tube,  2.5  cm.  in  diameter  and  4  cm.  or  8  cm.  long.  The 
X-radiation  was  usually  directed  axially,  sometimes  obliquely,  against 
the  walls.  With  the  tube  8  cm.  long  measurable  coronas  were  not 
obtained,  no  matter  whether  the  rays  passed  axially  through  the  fog 
chamber  or  not.  In  the  absence  of  the  lead  screen,  or  when  the  lead 
screen  was  replaced  by  a  thin  continuous  aluminum  screen,  the  nuclei 
often  filled  the  chamber  on  the  A  and  the  B  sides  and  the  coronas 
were  large.  This  would  again  be  accepted  as  evidence  favoring  the 
view  that  the  nuclei  come  out  of  the  walls ;  but  when  the  radiation  is 
directed  against  these  walls  through  the  tube  there  is  no  appreciable 
increment.  Thus  the  experiments  remain  inconclusive. 

The  work  was  now  continued  by  cutting  down  the  tube  to  4  cm.  in 
length.  The  strong  coronas  obtained  were  clear  and  round,  with  very 
little  fog.  At  times  they  seemed  to  be  largest  in  the  middle  of  the 
apparatus.  Slight  oval  distortion  appeared  on  the  A  side  near  the 
bulb  only.  The  general  absence  of  distortion  when  the  impact  of 
X-rays  is  cut  off  from  the  top  and  the  bottom  again  is  favorable  to 
an  origin  of  nuclei  in  those  parts.  Failure  of  the  experiments  18  to  21 
is  attributable  to  the  spark  gap  of  the  coil ;  but  here  coronas  were 
often  seen  throughout  the  length  of  the  fog  chamber,  very  gradually 
decreasing  in  size  from  A  to  B.  When  the  eye  was  moved  rapidly  in 
this  direction,  the  coronas  were  found  to  lie  within  a  triangle,  sym- 
metrical with  respect  to  the  axis  of  the  fog  chamber,  and  the  diameter 
of  the  coronas  vanishes  at  the  apex  of  the  triangle,  near  the  middle 
of  the  chamber,  as  suggested  in  figure  i . 

14.  Continued,  with  change  of  apparatus. — In  these  experiments  a 
more  powerful  coil  was  used,  actuated  by  six  storage  cells  and  a 
Foucault  interrupter.  The  object  first  aimed  at  was  a  contrast  of  the 
rays  entering  the  fog  chamber  axially  with  the  oblique  rays  which 
strike  the  walls.  Accordingly,  in  experiments  22  to  24  the  entrance 


14         NUCLEATION   OF  THE   UNCONTAMINATED  ATMOSPHERE. 

of  radiation  into  the  axial  part  of  the  end  of  the  fog  chamber  is  cut 
off  by  a  lead  disk,  /},  figure  12,  about  2.5  cm.  in  diameter.  In  com- 
parison with  experiment  27,  where  the  screen  was  removed,  the  coronal 
effect  for  the  disk  is  somewhat  weaker,  but  throughout  of  the  same 
nature,  with  campanulate  or  spindle-shaped  coronas  filling  more  than 
half  of  the  length.  Much  rain  and  fog  were  present,  and  crimson- 
colored  streamers  stretched  horizontally  and  symmetrically ,  bow-shaped 
(convexity  outward),  from  end  to  end.  The  first  coronas  (sj  are  not 
measurable,  but,  after  the  first  fog  particles  have  fallen  out,  the 
second  (s2)  are  quite  so,  being  round  and  clear. 


i 

3B 


FIGS.  11-12. — Fog  chambers  with  screens  and  X-ray  bulb. 

The  disk  was  now  removed  and  a  lead  screen ,  S,  figure  1 1 ,  with  a  hole 
about  2.5  cm.  in  diameter,  placed  over  the  end  of  the  fog  chamber,  with 
the  X-ray  bulb  placed  as  before.  To  make  the  wood  more  transparent 
a  waxed  cork  was  inserted,  giving  free  entrance  to  the  axial  rays.  All 
screens  were  earthed  as  usual.  Experiments  25  and  26  show  the 
results.  The  contrast  with  the  preceding  is  marked.  The  coronas 
are  round,  and  in  the  first  exhaustion  show  apertures  (s^  decidedly 
smaller  than  the  coronas  obtained  in  the  second  exhaustions  of  the 
preceding  cases.  True,  the  amount  of  radiation  entering  the  fog 
chamber  is  much  larger  for  the  case  of  the  disk  than  for  the  case  of  the 
perforated  screen;  but  it  nevertheless  follows  that  the  axial  rays,  even 
if  entering  under  favorable  conditions,  can  not  be  specially  efficient. 
Rays  which  have  penetrated  the  fog  chamber  obliquely  and  impinge 
on  the  top  and  bottom  are  responsible  for  nearly  the  whole  of  the 
dense  fog  usually  observed. 

In  further  experiments,  work  with  the  flanged  lead  tube  (2.5  cm.  in 
diameter,  4  cm.  long,  figure  10,  center  of  bulb  5  to  6  cm.  from  the  end 
of  the  fog  chamber  and  about  8  cm.  from  the  inner  face)  was  resumed 
and  successively  placed  in  positions,  a  (axial),  /  (radiation  grazing  the 
top  surface),  b  (radiation  grazing  the  surface  of  water  below,  as  seen 
in  figure  1 1),  the  screen  being  moved  with  the  bulb.  The  experiments 


AXIAL   AND   OBLIQUE   RADIATION. 


28,  30,  33,  and  34  are  deficient  from  the  gradual  loss  of  strength  of  the 
X-ray  bulb;  but  the  data  for  s  in  the  axial  case  are  nevertheless  larger 
than  for  the  cases  where  the  rays  grazed  the  top  or  the  bottom  of  the 
fog  chamber.  In  the  latter,  the  corona  is  particularly  small  and  open 
on  top,  showing  the  absence  of  nuclei  in  the  upper  strata  of  the  air  of 
the  fog  chamber.  Thus  the  endeavor  to  directly  call  out  the  nuclei 
from  the  top  or  the  bottom  of  the  fog  chamber  has  again  failed. 


C 


a 


FIG.  13. — Fog  chamber  with  axial  and  oblique  radiation. 

A  final  test  on  the  effect  of  the  walls  was  made  in  a  somewhat  dif- 
ferent manner  by  placing  the  bulb  at  a  distance  of  80  cm.  from  the 
chamber  C,  figure  13,  at  first  axially,  as  shown  at  #,  and  then  in  the 
raised  position,  b.  In  the  first  instance  the  rays  pass  through  the 
least  surface  of  wood  and  the  incidence  within  is  grazing;  in  the  second 
(nonaxial),  the  rays  pass  through  a  much  larger  surface  of  wood  and 
the  incidence  is  at  a  large  angle.  Table  9  shows  the  results  in  the  two 
cases  to  be  identical,  barring  increased  distance  and  the  tendency  of 
the  bulb  to  lose  efficiency  in  the  lapse  of  time.  In  the  present  case, 
however,  the  nuclei  are  of  the  fleeting  kind  discussed  in  the  chapters 
below,  and  comparison  with  the  above  persistent  nuclei  is  not  at  once 
permissible. 

TABLE  9. — Comparison  of  axial  end  oblique  rays  5^  =  23.3  cm. 


Position  of  bulb. 


Remarks. 


Axial 

Raised  

Raised  

Axial 

Raised  

Axial 

Axial 

Raised  35  cm 

Raised  55  cm 

Raised  55  cm 

Axial 


3-6 
3-6 
3-5 

*3'6 
*5-3 
4-6 
t4-o 
t4-o 
t3-8 
t3-8 


Distance,  80  cm.  from  bulb  to  chamber  (inside)  axially. 
Raised  position  35  cm.  above  axis.  Rays  off,  5=0.0 
(fig.  13).  Observations  made  during  exposure  to  X-rays. 

Distance,  40  cm. 


Distance,  $  80  cm.     8^  =  24.  8cm.     Exposure,  3  min. 


*  Periodicity.     Difference  due  to  X-ray  bulb. 


fAir  5  = 


1 6         NUCLEATION   OF  THE  UNCONTAMINATED   ATMOSPHERE. 

15.  Conclusion. — Generally,  when  the  bulb  is  close  to  the  end 
of  the  chamber,  the  coronas  obtained  after  a  short  exposure  are  all 
roundish,  but  taper  from  a  large  size  near  the  bulb  to  the  vanishing 
diameter  or  apex,  figure  i,  near  the  middle  of  the  fog  chamber,  with 
all  intermediate  gradations  of  aperture  in  corresponding  intermediate 
positions.  The  pressure  difference,  &p,  applied  is  thus  more  and  more 
in  excess  of  the  fog  limit  as  the  line  of  sight  is  nearer  the  bulb. 
Beyond  the  apex  the  pressure  difference  used  is  below  the  fog  limit. 
Smaller  nuclei  occur  throughout  the  chamber,  but  they  are  probably 
more  and  more  fleeting  in  character.  The  colloidal  nuclei  of  dust-free 
air  are  always  present.  The  number  of  nuclei  within  the  given  range 
of  condensation,  /.  e.,  above  a  certain  lower  limit  of  diameter,  increases 
with  the  intensity  of  the  ionization,  axially  as  well  as  transversely. 
If  the  exposure  is  prolonged  and  the  radiation  sufficiently  intense, 
the  nuclei  are  everywhere  within  the  given  pressure  difference,  but 
the  axial  excess  of  efficient  nuclei  is  retained.  Beyond  this,  the 
endeavor  to  come  to  a  decision  as  to  the  origin  of  the  persistent  nuclei 
on  the  basis  of  the  above  experiments  seems  as  yet  premature ;  for  in 
addition  to  the  hypothesis  which  refers  them  to  the  impact  of  X-rays 
on  the  walls  of  the  vessel,  the  diffusion  hypothesis,  the  effect  of  sec- 
ondary radiation  within  the  vessel  (such  radiation  outside  of  the  vessel 
produces  fleeting  nuclei  only  as  will  be  detailed  in  Chapter  III),  etc., 
there  is  something  to  be  said  in  favor  of  the  spontaneous  production 
of  water  nuclei  in  the  presence  of  the  intense  X-radiation  arriving  at 
any  point  from  both  primary  and  secondary  sources. 


CHAPTER  II. 

NUMBERS  AND  GRADATIONS  OF  SIZE  OF  NUCLEI  IN 
DUST-FREE  AIR. 

EXPERIMENTS  WITH   DUST-FREE  AIR   NOT  ADDITIONALLY  ENERGIZED. 

Alternations  of  large  and  small  coronas  observed  in  case  of  identical 
condensations  produced  in  dust-free  air  saturated  with  moisture. 

16.  Apparatus. — By  dust-free  air  I  mean  air  which  has  been  passed 
through  a  packed-cotton  filter.  My  filters  are  16  inches  long,  conical, 
tapering  from  about  2  inches  in  diameter  at  the  large  end  to  about 
^  inch  at  the  other.  They  contain  absorbent  cotton  rammed  in  from 
both  ends  and  kept  in  place  by  wire.  When  filtered  air  is  required, 
the  stopcock  is  only  just  opened  so  that  influx  of  dust-free  air  may 
be  extremely  slow.*  This  insures  proper  filtration  and  does  not 
interfere  with  the  saturation  of  the  air  in  the  fog  chamber.  In  this 
section  condensation  was  produced  in  a  long  glass  cylinder,  16  inches 
from  end  to  end  and  5^  inches  in  diameter,  placed  horizontally  and 
normal  to  the  line  of  sight.  It  contained  a  rectangular  framework 
of  copper  wire  covered  with  wet  cotton  cloth,  except  on  the  two 
opposed  broadsides  through  which  the  coronas  were  observed.  The 
distance  between  the  bottom  (water)  and  the  roof  of  the  rectangular 
framework  was  about  9  cm.  The  provisions  for  keeping  the  air 
saturated  are  thus  ample. 

The  vacuum  chamber  was  a  large  boiler  of  galvanized  iron, 
having  a  capacity,  V,  of  over  100,000  cc.,  while  the  capacity,  v,  of 
the  condensation  chamber  is  about  6,700  cc.,  so  that  the  volume 
ratio,  v\V,  is  but  0.063.  The  two  chambers  are  connected  by 
about  a  foot  of  rubber  tubing  over  i  inch  in  bore,  usually  containing 
a  i -inch  plug  gascock.  An  instantaneous  clapper  valve  of  the  same 
dimensions  and  opened  with  a  hammer  was  often  used  for  comparison. 

Later  the  glass  fog  chamber  was  advantageously  replaced  by  one  of 
waxed  wood  (see  fig.  i,  Chapter  I),  with  the  opposed  sides,  through 
which  the  coronas  were  observed,  made  of  plate  glass.  The  internal 
dimensions  in  this  case  were  55X12X20  cc.,  and  the  volume  ratio > 
v\V,  in  connection  with  the  vacuum  chamber,  about  0.13.  There 
is  difficulty,  however,  in  using  a  chamber  of  this  kind  for  the  present 
purposes,  where  even  very  small  leakage  is  a  serious  discrepancy. 

*  When  the  rate  of  filtration  is  gradually  decreased  until  it  all  but  vanishes,  results 
of  special  interest  are  observed  which  will  be  detailed  elsewhere. 

17 


1 8         NUCLEATION    OF  THE   UNCONTAMINATED   ATMOSPHERE. 

If.  Manipulation— Fog:  limit.— The  experiments  were  conducted  as 
follows :  Having  selected  a  suitable  pressure  difference  above  that  at 
which  condensation  in  dust-free  air  just  begins  (usually  termed  the 
"  fog  limit  "  in  the  present  paper),  the  dust-free  moist  air  in  the  closed 
condensation  chamber  at  atmospheric  pressure  is  suddenly  exhausted 
and  the  corona  measured.  After  all  fog  has  subsided  the  exhaustion 
cock  is  closed  and  the  filtered  air  very  slowly  admitted.  The  opera- 
tions are  then  repeated,  allowing  time  (about  2  to  3  minutes)  for 
saturation.  Under  all  circumstances  the  treatment  for  large  and 
small  coronas  was  identical. 

In  the  given  apparatus  condensation  in  dust-free  moist  air  began  at 
the  pressure  difference,  S/>  — 22.5,  corresponding  to  the  volume  expan- 
sion of  about  1.43.  The  pressure  difference  usually  applied  in  the 
experiments  was  8^  =  31.2,  and  the  volume  expansion  1.72. 

18.  Alternations  of  large  and  small  coronas  (periodicity  of  inferior 
and  superior  coronas). — The  small  coronas  are  usually  sharp,  but  the 
large  coronas  appear  blurred  and  filmy,  accompanied  with  much  rain. 
Remembering  that  all  operations  are  conducted  in  a  way  strictly  the 
same,  table  10  (pp.  19-20)  shows  the  coronas  seen  in  the  successive 
exhaustions.  The  angular  diameter  or  aperture  is  sin  <£/2  =  5/60,  or 
nearly  ^  =  5/30.  The  eye  at  the  goniometer  was  about  40  cm.  from 
the  axis  of  the  condensation  chamber  (placed  as  close  as  possible  to 
insure  clearer  vision)  and  the  source  of  light  250  cm.  beyond  it. 
Observations  were  made  along  the  axis  of  the  cylinder,  placed  hori- 
zontally. The  number  of  nuclei  per  cubic  centimeter  of  the  exhausted 
air  will  be  denoted  by  n,  while  N  shows  the  number  per  cubic  centi- 
meter of  air  at  normal  pressure.  The  reduction  of  n  to  TV  where  it  is 
not  essential  will  often  be  omitted. 

In  the  case  of  2 -minute  periods  between  the  exhaustions  the  perio- 
dicity is  maintained  without  exception  (fig.  14).  For  brevity  let  the 
smaller  coronas  be  called  inferior,  the  larger  coronas  superior.  Fre- 
quently a  very  small  inferior  corona  evokes  a  relatively  large  superior 
corona,  or  larger  inferior  coronas  are  followed  by  smaller  superior 
coronas  ;  but  this  is  not  always  the  case.  As  a  more  general  rule,  if 
the  aperture  is  intermediate  between  the  inferior  and  superior  coronas, 
the  succeeding  corona  is  of  the  same  size,  and  oscillation  terminates. 
In  part  III,  for  an  accidentally  more  rapid  influx  than  the  exceedingly 
slow  influx  of  filtered  air  in  the  earlier  parts  of  table  10,  this  is  initially 
the  case,  but  the  oscillation  is  soon  reestablished.  In  part  IV,  the  water 
was  shaken  so  as  to  wet  the  glass  sides  of  the  chamber,  but  without 
effect  on  the  oscillation  (fig.  15).  In  part  V  of  table  10,  the  original 
periodicity  is  again  wiped  out  by  accidental  influx  of  much  air  through 


ALTERNATIONS  OF  APERTURE. 


the  filter.  Periodicity  thereafter  fails  to  reappear,  as  is  also  the  case  in 
parts  VI  and  VII.  Similar  cases  occur  in  parts  VIII,  IX,  and  X.  The 
mean  apertures  at  25°,  20°,  and  n°  do  not  differ  sufficiently  to  indicate 
a  temperature  effect  above  the  value  of  the  incidental  errors. 

TABLE  10. — Periodicity  in  the  condensation  of  dust-free  air.     Plug  valve.     Pressure 
difference,    8^=31.2    cm.     Temperature  =  25°  C.     Glass   clear,    no   shaking  of 


water  needed.     Two-minute   periods  between   exhaustions, 
drical  fog  chamber,  volume  ratio  v\V  =  0.063. 


Slow  influx.     Cylin- 


Exhaust 
No. 

s. 

j*«rt 

Exhaust 
No. 

S. 

.X»rt 

Exhaust 
No. 

5. 

.X«rt 

Part  I. 

Part  II—  Continued. 

Part  III. 

i 

2 

3 
4 
5 
6 

8 

5-7 

2-5 

6.4 
2.9 
6.6 

3-2 

2.3 

73 
6.1 

97 
9.6 
1  06 

12.6 

9 

5 
6 

8 
9 

IO 

ii 

12 
13 

15 

16 

18 
19 

20 

2.9 
6.4 

6.6 

6.4 

3-2 

6.6 
3-2 
6-3 

6.6 
3-5 
5-5 
3-o 
6.9 

9 
97 

IO 

1  06 
ii 
97 

12.6 

106 

12.6 

93 
ii 
106 
16.7 
67 

IO 
122 

22 

23 
24 

25 
26 

27 
28 

29 
30 

3-9 
3-8 

I'.s 

5-2 

6^3 
3-4 
5-9 

59 
58 
47 

88 

47 
79 
47 
96 
52 
90 

Part  II. 

I 

\ 

2.9 

6.2 

3-4 
5-3 

9 
90 

15 
59 

*After  i6h  (left  over  night).  t  After  25m. 

t  Accidental  rapid  influx.     Note  the  rise  of  inferior  coronas. 

TABLE  10,  continued. — Slow  influx;  water  shaken;  fog  in  glass;  20°  C.;  8^  = 


Exhaust 
No. 

5. 

wXio-3. 

Exhaust 
No. 

5. 

wXio"3. 

Exhaust 
No. 

s. 

wXio~3. 

Part  IV. 

Part  V. 

Part  VI.  —  Temperature, 
11°  C.      8^=31.2. 

*i 

2 

3 

4 

6 

7 
8 

9 

10 

ii 

12 
13 

J4 
15 

«•? 

5-2 

2.8 

5-3 

2.4 

5-9 
3-o 
5-7 
2-9 
5-5 

2.8 

5-6 

2.8 

5-4 

2.8 

2-3 

56 
7-9 
59 
5-o 

82 

10 

73 
9.0 
67 

7-9 

70 

7-9 

64 

7-9 

i 

2 

tu 

1 

2-3 

5-7 
3-0 
4.1 
4.2 
5-3 

5-2 

3-5 
73 
10 
26 
29 
59 
56 

ti 

2 

3 

4.6 
4.6 

4.6 

39 
39 
39 

Part  VII.—  Temperature, 
11°  C.      8^  =  29.8. 

tfi 

3 

U 

3-9 
4-7 
4.6 

4-7 

23 

42 

39 
42 

Left  after  ish.  f  Periodicity  absent  in  the  first  case  after  accidental  influx. 


20        NUCLEATION   OF  THE  UNCONTAMINATED  ATMOSPHERE. 
TABLE  10,  continued. — 24-25°  C.     Cylinder.     5^  =  31.2.     Promiscuous  results. 


Exhaust 
No. 

s. 

wXio-3. 

Exhaust 
No. 

s. 

«Xio~3. 

Exhaust 
No. 

5. 

WXIO-3. 

Part  VIII. 

Part  IX. 

Part  X. 

i 

*3-o 

10 

i 

t3-3 

14 

i 

t3-5 

»7 

2 

4-9 

49 

2 

5-3 

59 

2 

5-2 

56 

3 

4-5 

36 

3 

3-0 

10 

3 

2-5 

6.1 

4 

4-7 

43 

4 

5-7 

73 

4 

6.1 

85 

5 

4-7 

43 

5 

2.7 

7-9 

5 

**2.8 

7-9 

6 

5-7 

73 

6 

5-4 

64 

7 

2.7 

7-9 

7 

4-2 

29 

8 

5-2 

56 

9 

4.8 

46 

10 

4.9 

49 

ii 

4-9 

49 

12 

4.8 

46 

*  After  24  hours.  f  After  15  hours. 

**  Apparatus  (water)  shaken,  thereafter  glass  dull. 


\  After  2  hours. 


In  table  1 1 ,  for  3-minute  periods  between  the  exhaustions  as  a  safe- 
guard against  partial  saturation,  the  same  oscillations  reappear  (fig. 
17).  Very  small  inferior  coronas  are  again  followed  by  the  larger 
superior  coronas.  On  the  other  hand,  the  larger  superior  coronas  usu- 
ally precede  larger  inferior  coronas,  as  above.  The  case  of  5 -minute 
periods  between  the  exhaustions  (fig.  18)  begins  with  marked  perio- 
dicity, after  which,  however,  cotemporaneously  with  the  deposition  of 
fog  on  the  glass  between  observations,  periodicity  vanishes. 

TABLE  ii. — Periodicity  in  the  condensation  of  dust-free  air.     Plug  valve.     §^  =  31.2. 

Temperature  =  25°  C. 


Exhaust 

Exhaust 

Exhaust 

No. 

nXio 

No. 

5. 

wXio    . 

No. 

5. 

nXio    . 

Five-minute  periods  (and 

Three-minute  periods  between  exhaustions. 

longer)  between  exhaus- 

tions. 

i 

2.9 

9 

7 

3-i 

II 

i 

59 

82 

2 

5-7 

73 

8 

5.8 

76 

2 

2-7 

7-9 

3 

3.0 

10 

9 

3-2 

12.6 

3 

5.6 

90 

4 

5-9 

82 

10 

6.2 

90 

4 

*4-4 

46 

5 

2.8 

7-9 

ii 

3-2 

12.6 

5 

*4.8 

59 

6 

6.4 

126 

6 

61 

*  Glass  fogged  during  the  interval. 


ALTERNATIONS  OF  APERTURE — DECAY. 


21 


Ob.& 


8p.*r 


ZfaJfr.  I  £ 


8          10         /£         14-         18         18          RO 


77          73          75     1  5 


FIGS.  14-18. — Graphs  showing  the  alternations  of  the  apertures  (s)  of  coronas  in  non- 
energized  dust-free  air.  The  abscissas  show  the  numbers  of  the  successive 
exhaustions;  the  ordinates  are  nearly  as  the  cube  roots  of  the  number  of  effi- 
cient nuclei. 

FIG.  19. — Decay  of  the  nuclei  examined  in  the  lapse  of  hours. 

Table  i,  referred  to  in  figs.  14,  15  and  16,  will  be  found  as  table  10,  p.  19. 
Table  2,  referred  to  in  figs.  17  and  18,  will  be  found  as  table  n,  p.  20. 
Table  3,  referred  to  in  fig.  19,  will  be  found  as  table  12,  p.  22. 

19.  Effect  of  lapse  of  time  on  the  nucleation  of  dust-free  air  impris- 
oned in  the  fog  Chamber. — The  5-minute  periods  in  the  preceding  table, 
or  figure  18,  do  not  markedly  diminish  the  aperture  of  the  coronas. 
Larger  periods  of  waiting  are  very  effective,  as  is  seen  in  table  12, 
where  vj  V shows  the  volume  ratio  of  fog  and  vacuum  chambers.  The 


NUCIvEATlON   OF  THE   UNCONTAMINATED   ATMOSPHERE. 


measurements  refer  to  an  initial  large  corona  of  say  5  =  5  cm.;  but  as 
this  can  not  be  measured  without  destroying  the  nuclei,  the  present 
data  merely  show  the  usual  occurrence  of  inferior  coronas  in  the  lapse 
of  time  (fig.  19).  In  15  hours  the  aperture  is  reduced  to  one-third  and 
the  nucleation  possibly  to  one-thirtieth.  Certain  relatively  high 
results  at  the  end  of  the  table  seem  to  be  referable  to  the  presence  of 
radium  in  the  laboratory,  but  no  definite  statement  can  be  made. 

TABLE  12. — Evanescence  of  nucleation  of  dust-free  air  in  lapse  of  time. 


Glass  fog  chamber.     *v{V=  0.063. 

Wooden  fog  chamber. 

5  A 

Temp. 

Time 

S. 

.XXO-3 

Temp. 

Time 

s. 

*XlO-3 

5  p. 

Time 

, 

.**• 

31  .2 

°C 

h.  m. 

oc 

h.  m. 

•c. 

h.  m. 

ii 

o     o 

(4-6) 

(70) 

20 

0      0 

(5.5) 

(67) 

t33-o 

0 

20 

2.6 

3-9 

I       0 

2.4 

5-o 

24 

3.0 

10.3 

20 

0      0 

(5-2) 

(56) 

23 

o    o 

(5.5) 

(67) 

o 

3-4 

15-6 

15     o 

1.7 

2-3 

3     o 

2.3 

4.1 

o 

3-3 

14-5 

20 

o     o 

(5-2) 

(56) 

25 

o     o 

(5.5) 

(67) 

2       O 

1,8 

2.4 

16    o 

1.7 

2-3 

2O 

O      O 

(5-5) 

(67) 

24 

3-o 

10 

o  50 

2-5 

6.1 

3-3 

14 

*  Volume  ratio  of  fog  and  vacuum  chambers.      f  Vacuum  chamber  disconnected. 

The  marked  occurrence  of  inferior  coronas  in  the  lapse  of  time 
(under  conditions,  therefore,  where  the  air  must  be  saturated  with 
moisture)  seems  to  be  positive  proof  against  the  view  that  these  coro- 
nas owe  their  origin  to  undersaturation.  The  corona  immediately 
following  (second  exhaustion)  is  always  a  superior  corona.  One  may 
note  that  if  extremely  fine  nuclei  (colloidal  molecules)  pass  the  filter, 
a  time  loss  like  the  present  would  accompany  their  decay. 

20.  Effect  Of  pressure  difference  on  exhaustion. — The  reason  for  irreg- 
ular results  in  tables  13,  14,  and  15  is  now  apparent,  for  in  these  experi- 
ments the  tendency  to  periodicity  was  not  yet  understood.  Nor  can  it 
in  any  case  be  effectually  combatted.  After  the  fog  chamber  has  been 
cleared  of  foreign  nuclei,  which  occurs  at  a  pressure  difference  above 
20  cm.  of  mercury  and  at  about  the  same  volume  expansion  in  both 
chambers,  the  effect  of  further  increasing  the  pressure  difference,  8/>,  is 
an  exceedingly  rapid  increase  of  the  apertures  of  coronas.  The  first 
coronas  after  the  air  is  made  dust-free  are  usually  particularly  large. 
Though  this  looks  like  a  foreign  effect,  it  is  probably  due  to  periodicity. 


INCREASING   SUPERSATURATION. 


Very  soon,  however,  the  effect  of  8/»  ceases  to  increase  the  apertures. 
All  the  ^-curves  either  pass  through  a  maximum  or  reach  a  limiting 
asymptote,  as  is  particularly  marked  in  case  of  table  15  (figs.  20  and 
21).  The  fog  limit  lies  a  little  lower  in  case  of  the  large  chamber  (wood, 
vlV=o.i3)  than  in  the  case  of  the  small  chamber  (glass,  z>/F=o.o63), 
an  anomalous  result,  since  the  latter  condensation  must  be  the  swifter. 
There  does  not  seem  to  be  any  adequate  effect  for  the  relative  sudden- 
ness of  condensation  in  the  two  cases.  The  last  parts  of  table  13  con- 
tain examples  in  which,  with  the  same  apparatus  and  apparently 
under  identical  conditions  (dew  on  one  side  of  the  glass),  a  steady  and 
thereafter  an  oscillating  aperture  is  encountered.  The  last  series  gives 
an  instance  of  oscillations  which  vanish  when  the  water  in  the  fog 
chamber  is  shaken  from  side  to  side. 

TABLE  13. — Effect  of  pressure  difference.     Long  condensation  chamber.      v  =  55X12 
X 20  =13, 200   cm.3,   for   fog  chamber;   F=  106,000  cm.3,   for  vacuum  chamber 
13,200 


v\V-- 


106,000 


=  0.125.  Instantaneous  valve.  Goniometer  85  cm.  from  fog  chamber. 


*/. 

s. 

.VXio-3. 

t* 

s. 

WXio-3. 

Outgoing. 

Returning. 

19.6 

0.0 

0.0 

33-o 

2.O 

5-9 

24.2 

1.8 

3-7 

29.2 

2.9 

19.8 

24.2 

1.8 

3-7 

25.8 

i-5 

3-1 

28.3 

3-o 

21.5 

22.7 

•9 

1.9 

32.7 

3-0 

25-9 

20.0 

.0 

.0 

37-4 

3-i 

33-7 

TABLE    14. — Cylindrical  condensation  chamber.     v/V=o,o6.     Instantaneous  valve.. 
Goniometer  85  cm.  from  fog  chamber. 


1* 

5. 

A^Xio-3. 

I* 

5. 

NX  lo-3. 

Outgoing. 

Outgoing. 

18.8 

o.o 

0 

35-i 

2-5 

16 

20.4 

0.0 

o 

42.6 

2.6 

24 

20.7 

0.0 

o 

52.2 

3.5 

IO2 

25-6 

*4-i 

84 

*  Initial  excess. 


24         NUCLEATION    OF  THE   UNCONTAMINATED  ATMOSPHERE. 


TABLE  15. — Cyclic  variation  of  pressure  difference.    Cylindrical  condensation  chamber. 
v/y=o.o6.    Plug  valve  (i-inch  bore).     Goniometer  85  cm.  from  fog  chamber, 


I* 

,. 

A*,0-. 

* 

* 

J*«rt 

Outgoing. 

Returning. 

15-2 

0.0 

0 

48.9 

4.1 

136 

18.5 

0.0 

0 

46.3 

3-6 

77 

20.9 

(?) 

o 

43-3 

3-7 

72 

20.  i 

0.0 

o 

40.8 

2.9 

32 

20.  2 

(?) 

o 

38.4 

4-5 

no 

26.2 

*4.o 

46 

35-7 

31 

26.2 

2.4 

9.6 

33-5 

5-o 

126 

26.2 

2.5 

ii 

30.8 

3-2 

29 

36.6 

3-2 

36 

28.9 

3-4 

33 

36.6 

3-2 

36 

27.0 

1.9 

4.9 

43-7 

4.2 

"3 

24.7 

1.8 

3-7 

43-7 

4-3 

123 

23.1 

1.3 

2-3 

3-7 

112 

21.8 

?  o.o 

o 

20.  6 

o.o 

o 

19-5 

o.o 

o 

*  Initial  excess. 

TABLE  16. — Effect  of  pressure  difference.  Cylindrical  condensation  chamber.  In- 
stantaneous valve.  Eye  at  goniometer,  85  cm.  from  fog  chamber,  ^reduced  to 
normal  atmospheric  pressure. 


dp. 

5. 

AOOo-3. 

»* 

.s. 

A^Xio-3. 

20.  1 

0.0 

0 

34-7 

5-0 

132 

20.5 

0.0 

o 

34-9 

2.7 

20 

20.7 

0.0 

0 

34-8 

5-i 

140 

23-3 

3-o 

18 

34-8 

2.6 

18 

34-8 

5-i 

140 

26.1 

2.2 

7 

34-8 

2.7 

20 

26.3 

4.0 

46 

43-6 

*5-4 

237 

26.2 

2.6 

12 

43-5 

5-i 

2O2 

26.2 

4.I 

50 

43-5 

5.8 

279 

26.2 

2.2 

7 

43-5 

3-0 

41 

26.2 

4-3 

58 

26.2 

2.6 

12 

*  Valve  injured. 

In  table  16  the  occurrence  of  marked  periodicity  gives  rise  to  two 
distinct  ^-curves,  both  of  which  soon  approach  an  asymptote  (figs.  22, 
23).  In  the  last  group  of  observations  the  alternations  are  not  regu- 
lar (leakage  of  valve),  but  the  extremes  are  indicated.  Differing  from 
this,  the  results  of  table  17  in  the  outgoing  series  of  apertures  (Sfi, 
increasing)  are  remarkably  free  from  periodicity  and  show  a  tendency 
to  pass  through  a  maximum.  In  the  return  series  much  fresh  air  was 
drawn  through  the  filter  into  the  fog  chamber  and  thence  into  the 


INCREASING    SUPERSATURATION. 


vacuum  chamber.  It  is  noteworthy  that  very  large  coronas  are  then 
met  with  on  first  exhaustion,  a  result  which  may  bear  on  the  expla- 
nation of  periodicity. 

In  table  17  (figs.  24,  25)  the  goniometer  was  moved  close  to  the 
fog  chamber  to  insure  clearer  vision.  The  chart  (figs.  20-25)  on 
page  26  shows,  n,  the  number  of  nuclei  per  cubic  centimeter  of  the 
expanded  air;  in  the  tables  the  number,  N,  reduced  to  air  at  normal 
pressure  and  temperature  is  usually  given. 


TABLE  17. — Cyclic  variation  of  pressure  difference.     Cylindrical  fog  chamber, 
valve.     Eye  at  goniometer,  50  cm.  from  axis  of  cylinder. 


Plug 


I* 

5. 

NX  10  ~3. 

**. 

S. 

AXio~3. 

Outgoing. 

Returning. 

19-5 

o.o 

o 

43-8 

5-3 

171 

26.2 

5.8 

105 

26.5 

5.8 

106 

35-3 

*7.i 

267 

26.2 

5-5 

94 

35-3 

5-2 

H3 

26.2 

5-8 

105 

35-3 

6.4 

194 

35-4 

6.6 

211 

26.5 

*5-5 

94 

35-o 

6.6 

209 

26.3 

4-7 

59 

26.3 

4.9 

67 

44.2 

5-6 

207 

43-8 

5-6 

203 

24.0 

36 

24 

43.8 

5.6 

203 

22.8 

i-5 

2-5 

22.2 

o.o 

o 

52.3 

5.6 

297 

20.5 

o.o 

o 

52.4 

5-o 

215 

18.0 

o.o 

0 

52-4 

4-9 

209 

*  Nuclei  probably  enter  from  large  influx  of  air  through  filter.  Therefore  next 
coronas  are  small  from  undersaturation  and  periodicity.  These  fine  nuclei  get 
gradually  out  of  reach  as  Sp  decreases. 

21.  Remarks  on  the  tables.— It  will  conduce  to  clearness  to  take 
the  last  tables  showing  the  increase  of  apertures,  s,  with  the  increase 
of  presure  difference,  8p,  first  in  order.  All  the  s-curves,  figures  20-25, 
either  pass  through  a  maximum  or  reach  an  asymptote.  If  the 
exhaustion  is  insufficient  the  groups  of  smaller  nuclei  will  escape 
precipitation  and  the  coronas  be  relatively  small.  This  will  also 
occur  if  relatively  large  nuclei  are  accidentally  present.  After  all 
nuclei,  large  and  small,  are  caught,  higher  sudden  exhaustion  can  no 
longer  increase  the  apertures.  More  water  is  instantaneously  precipi- 
tated per  cubic  centimeter.  Nevertheless  this  counter-effect,  if  it  is 
such,  will  also  vanish  with  increasing  pressure  differences,  because  of 
the  accentuated  rapidity  of  thermal  radiation .  The  adiabatic  method 


26         NUCLEATION   OF   THE   UN  CONTAMINATED   ATMOSPHERE. 

ceases  to  be  effective.  Finally  the  necessity  of  producing  sudden 
cooling  simultaneously  with  extreme  dilatation  is  a  complication ;  for 
in  view  of  the  relative  slowness  of  diffusion,  it  will  eventually  be  im- 
possible to  keep  the  instantaneously  dilated  water  vapor  saturated 
without  arresting  the  growth  of  the  fog  particles.  Above  Bp  =  40  cm. 
the  effect  of  sudden  exhaustion  might  actually  dry  the  air,  seeing  that 
the  density  of  vapor  is  instantly  reduced  more  than  one-half.  It  is 
thus  conceivable  that  even  slight  differences  of  supersaturation  at  the 
outset  may  show  themselves  effectively  at  these  high  exhaustions.  In 
table  1 6,  however,  the  nucleation  N  (reduced  to  normal  pressure) 
increases  almost  linearly  with  the  pressure  difference  even  at  the  high- 
est exhaustions.  The  evaporation  of  the  smaller  fog  particles  is 
probably  an  essential  part  of  the  whole  phenomenon. 


FIGS.  20-25. — Change  of  apertures  (s)  of  coronas  and  number  of  efficient  nuclei  («) 
varying  with  different  pressure  differences  (8p)  for  the  cases  of  superior 
and  inferior  coronas.  Dust-free  air. 

Table  6,  referred  to  in  fig.  20,  will  be  found  as  table  15,  p.  24. 

Table  7,  referred  to  in  fig.  22,  will  be  found  as  table  16,  p.  24. 

Table  8,  referred  to  in  fig.  24,  will  be  found  as  table  17,  p.  25. 


NUCLEATION   UNDER  VARYING   CONDITIONS.  27 

22.  Blurred  coronas. — The  occurrence  of  an  abundance  of  rain  with 
all  the  coronas,  as  well  as  the  blurred  appearance  of  the  coronas  them- 
selves, shows  that  gradation  of  particles  is  a  characteristic  feature  with 
all  these  condensations.     The  following  results  for  periodicity  appar- 
ently indicate  the  presence  of  a  group  of  markedly  large  particles  in 
the  amount  of  about  one-eighth  or  more  of  the  total  number  of  nuclei. 

23.  Time  effect. — In  the  lapse  of  time  exceeding  even  half  an  hour 
the  aperture  of  all  coronas  usually  diminishes  in  marked  degree .   Above 
the  fog  limit,  however,  the  coronas  do  not  vanish  as  the  result  of 
repeated  exhaustion,  i.  <?.,  the  air  can  not  be  freed  from  nuclei  by 
being  stored  in  a  closed  vessel  (fig.  19).    What  is  particularly  remark- 
able is  the  rapidity  with  which  nuclei  precipitated  by  condensation 
are  again  replaced.     Whether  these  come  through  the  filter  in  quasi- 
gaseous  form  (remembering  that  they  must  be  much  smaller  than  ions), 
or  whether  they  are  spontaneously  produced  in  the  imprisoned  air,  is 
yet  to  be  decided.     In  every  case  something  has  to  be  explained  away. 
If  the  nuclei  came  through  the  filter,  for  instance,  they  would  not 
come  through  periodically. 

24.  Oscillations  at  variable  pressure  differences.— With  increasing 
pressure  differences,  8/>,  the  superior  and  the  inferior  apertures  each 
lie  on  distinct  curves,  both  of  which  rise  rapidly  at  first,  are  then 
rapidly  retarded,  and  tend  to  reach  distinct  maxima  (figs.  20-25). 
The  limiting  ratio  of  apertures  is  liable  to  be  nearly  one-half.     If, 
however,  the  pressure  difference  is  carried  far  enough,  both  s-curves 
sometimes  change  character  by  decreasing  and  increasing,  respectively, 
eventually  to  reach  a  common  value.     If,  then,  pressure  difference 
is  in  turn  reduced  from  these  final  values,  the  oscillation  of  s  is  usually 
absent  and  a  mean  nucleation  appears  at  all  subsequent  (decreasing) 
pressure  differences. 

25.  Nucleations  at  varying  pressure  differences.— The  increase  of 
nucleation,  n,  with  the  pressure  difference,  8p,  is  difficult  to  interpret, 
since  the  inferior  and  superior  values  are  so  much  more  widely  and 
irregularly  distributed  (figs.  21,  23,  25).     The  ^-curves  usually  show 
two  limiting  rates  of  increase  of  n  with  8/>,  respectively  very  large  and 
very  small.     This  is  particularly  well  brought  out  in  the  data  of  table 
1 6   and  figure  23,  where  both  loci  are  nearly  straight  even  above 
8/>  =  40  cm.     They  become  more  so  if  the  nucleation  is  reduced  to 
normal  pressure,  as  shown  under  N.     Using  this  suggestion  the  data 
of  table  13  (wooden  fog  chamber)  are  largely  referable  to  inferior 
coronas.     With  one  exception,  this  is  also  the  case  in  table  14  for  the 


NUCLEATION   OF  THE   UNCONTAMINATED   ATMOSPHERE. 


glass  cylinder,  while  in  table  15  there  is  an  irregular  distribution  of 
observations  between  both  classes  of  curves.  In  table  17  inferior 
coronas  are  absent,  and  those  observed  present  an  accentuated  case  of 
superior  corona.  The  series  fails  to  detect  the  large  coronas  after 
8/>  =  35  cm.,  so  well  brought  out  in  table  16.  One  may  note  the  differ- 
ent valves  used. 

26.  Fog  limits. — An  interesting  feature  of  these  results  are  the  fog 
limits  or  pressure  differences  at  which  condensation  in  dust-free  air 
just  commences.  In  spite  of  the  different  sizes  of  apparatus  and 
valves  used,  the  fog  limits  are  about  the  same,  viz,  in  tables  13,  14, 
15,  16,  and  17. 


Table. 

5^= 

Apparatus. 

Valve. 

13 

22-23  cm- 

Wood,  t//F=.i3 

Plug. 

14 

21.5 

Glass,  z//F=.o6 

Clapper. 

15 

22-23 

<i          <  i          « 

Plug. 

16 

21-23 

II                      «                        II 

Clapper. 

17 

22-23 

Plug. 

These  results  are  surprising,  inasmuch  as  the  effect  of  the  volume 
ratio  of  fog  and  vacuum  chambers  and  the  valve  effect  would  naturally 
be  looked  to  as  productive  of  larger  differences.  With  other  appara- 
tus (Chapter  I)  the  data  were  : 


5p= 

Apparatus. 

Valve. 

22 
2O 

Wood,  vjV=  .7 
•7 

Plug. 
Clapper. 

Thus  the  supreme  importance  of  mere  rate  of  exhaustion  may  well 
be  called  in  question  until  more  definite  results  appear ;  for  with  so 
large  a  difference  of  volume  ratio,  valve  obstruction,  etc.,  the  essential 
features  should  appear  more  clearly.  It  is  possible  that  nuclei  of 
extreme  fineness  (colloidal  molecules)  may  pass  through  the  filter.  In 
such  a  case  these  would  capture  most  of  the  water  vapor,  reducing  the 
size  of  coronas  by  prohibiting  condensation  on  still  smaller  colloidal 
molecules.  Therefore,  if  the  filter  is  entirely  dispensed  with  and  a 
closed  vessel  used,  larger  coronas  may  appear  at  smaller  pressure 
differences. 


ALTERNATIONS  OF  APERTURE.  29 

2t.  Oscillations  at  fixed  pressure  differences.— Effectively  the  case 
of  oscillation  is  one  in  which  the  large,  sparsely  distributed  fog  par- 
ticles emit  more  nuclei  and  the  very  abundant  small  fog  particles 
fewer  nuclei,  i.  <?.,  the  phenomena  may  be  looked  upon  as  though 
the  nuclei  were  generated  during  the  growth  of  the  fog  particles. 
This  plausible  result,  however,  is  not  to  be  maintained  ;  for  the  emis- 
sion would  have  to  be  as  the  growth  of  surface — in  other  words,  as  the 
volume — and  the  number  of  particles  varies  inversely  as  their  volume. 
A  counter  supposition  may  be  hazarded  to  the  effect  that  the  fog  par- 
ticles of  large  coronas  absorb  more  nuclei  because  of  their  abundance 
than  the  fog  particles  of  small  coronas.  But  the  period  of  suspension 
of  particles  is  too  short  a  period  to  be  of  moment. 

If  negative  ions  are  more  active  as  condensation  nuclei  than  posi- 
tive ions,  the  results  observed  may  be  tentatively  grouped  in  accord- 
ance with  the  following  scheme  : 


V  V  V  V 

L,et  the  ions  be  originally  neutral  as  a  whole,  and  suppose,  as  in 
case  i ,  that  the  negative  ions  are  first  precipitated.  In  the  interval 
between  this  and  the  next  exhaustion  fresh  ions  are  generated  or  taken 
in  through  the  filter,  as  shown  in  case  2.  If  these  negative  ions 
partially  neutralize  the  positive  ions  left  over  in  case  i ,  the  second 
precipitation  takes  place  on  the  positive  ions.  Thereafter,  case  3,  the 
first  is  repeated,  etc.  But  if  the  coronas  are  taken  as  a  measure  of  the 
number  of  particles,  the  number  of  effective  nuclei  must  be  eight  times 
larger  in  the  first  case  than  in  the  second,  whereas  the  ions  should  be 
present  in  equal  numbers.  Hence  there  is  serious  objection  to  this 
hypothesis  at  the  outset,  quite  apart  from  the  absolute  numbers  in 
question,  which  are  enormously  too  large  to  be  referred  to  ions. 

28.  Undersaturation. — Some  mechanism  of  this  kind  is  nevertheless 
probable,  and  it  will  suffice  if  the  Undersaturation  produced  by  the 
precipitation  of  fog  particles  is  not  rapidly  made  up  by  diffusion  and 
convection,  or,  even  better,  if  water  nuclei  are  produced  by  evaporation 
of  fog  particles.  Of  the  above  hypotheses  that  of  Undersaturation  has 
broad  bearings  and  accounts  qualitatively  for  most  of  the  phenomena, 
as  will  presently  be  pointed  out  in  detail.  True,  the  large  coronas 


30        NUCLEATION   OF  THE  UNCONTAMINATED   ATMOSPHERE. 

must  be  supposed  to  carry  down  more  moisture  than  the  small  coronas, 
but  the  difference  need  not  be  great.  The  hypothesis  encounters  a 
serious  obstacle,  inasmuch  as  the  coronas  obtained  from  saturated  air 
which  has  been  imprisoned  for  long  intervals  of  time  (section  8)  are 
usually  an  extremely  small  type  of  inferior  corona,  whereas  they  should 
be  large  superior  coronas.  Long  intervals  of  waiting  between  exhaus- 
tions bring  out  not  a  superior  corona  but  at  best  one  of  intermediate 
size.  Another  precarious  feature  is  suggested  by  computating  the 
rate  at  which  saturation  should  be  established  in  the  most  unfavorable 
case  of  the  middle  air  layer,  between  the  wet  top  and  bottom  of  the 
fog  chamber,  for  diffusion  alone. 

In  fact,  if  diffusion  takes  place  from  the  wet  top  and  bottom  of  the 
rectangular  trough  of  height  a  into  a  partially  saturated  atmosphere 
of  initial  vapor  pressure  p0,  then  at  any  time  /,  at  the  middle  plate 
x  —  a\2. 

_Lsin*re-(3^)^  +  et    X 

32  / 

where  dp\dt  —  k  (cPpjdx*} .  Hence  if  a  =  1 1  cm . ,  as  in  the  largest  trough 
(wood),  and  if  £  =  0.23,  the  following  values  obtain  : 

^=  30         /0  =  o,^=.28       ^0  =  1/3,^  =  .  52        ^0  =  2/3,^=. 76 
60  .59  .72  .86 

120  .87  .gi  .96 

180  .96  .97  .99 

In  the  above  tables  a  was  usually  less  than  10  cm.  (glass  fog  cham- 
ber), making  the  condition  correspondingly  favorable. 

Hence  by  diffusion  alone  there  should  be  saturation  after  2  to  3 
minutes  even  at  the  most  distant  (middle,  x  =  a/2)  plane,  to  within  a 
few  per  cent,  for  the  central  layer  is  probably  always  more  than  half 
saturated  at  the  outset.  In  addition  to  diffusion,  however,  there  is 
marked  convection  due  to  the  lightness  of  water  vapor.  At  the  same 
time  there  is  no  evidence  that  the  more  numerous  but  small  drops  of 
the  superior  coronas  carry  down  a  sufficient  excess  of  water  ;  nor  are 
the  coronas,  though  blurred,  otherwise  distorted,  as  they  would  be 
for  a  definite  diffusion  gradient. 

29.  Undersaturation,  continued. — Assuming,  however,  that  under- 
saturation*  does  occur  and  is  oscillatory  as  the  result  of  successive 

*  It  will  be  shown  below,  Chapter  VI,  sections  97,  98,  that  the  probable  cause  of 
periodicity  is  not  Undersaturation  but  the  production  of  water  nuclei  by  the  evapora- 
tion of  the  small  fog  particles.  The  analysis  of  the  phenomena  given  in  section  14 
applies,  however,  with  obvious  changes,  to  both  cases,  and  has  therefore  been 
retained  in  the  text. 


ALTERNATIONS  OF  APERTURE.   .  31 

larger  and  smaller  precipitations,  the  cases  may  be  interpreted  in  suc- 
cession as  follows  : 

a.  The  superior  coronas  carry  down  more  moisture  and  should  be 
followed  by  even  larger  coronas,  and  vice  versa  ;  but  after  the  fog  par- 
ticles producing  the  superior  coronas  are  precipitated,  the  supersat- 
uration  possible   for   the   given   pressure  applied  no  longer  catches 
the  small  nuclei.     Hence  the  inferior  coronas  appear  in  succession. 
Hence,  also,  apart  from  what  may  be  time  errors  in  opening  the  stop- 
cock, very  large  pressure  differences  tend  to  wipe  out  the  oscillation, 
as  all  nuclei  are  caught. 

b.  The  ratio  of  i :  2  for  coronal  apertures  and  of  i  :8  for  the  volumes 
of  fog  particles  seems  out  of  keeping  with  the  slight  differences  of 
supersaturation  instanced  in  section  28;  but  this  is  again  a  question  of 
catching  the  group  of  smaller  nuclei. 

c .  The  phenomenon  is  much  too  definite  an  oscillation  of  aperture 
between  ^  and  2s  (nearly)  to  be  referable  to  an  irregular  cause  like 
deficient  supersaturation ;  but  the  two  types  of  nuclei  admit  of  a  wide 
range  of  saturation,  as  long  as  there  is  a  correspondingly  wide  dif- 
ference in  the  sizes  of  nuclei. 

d.  A  series  of  minor  observation  are  favorable  to  the  hypothesis  of 
residual  undersaturation  ;  as,  for  instance,  the  eventual  coalescence  of 
the  aperture  curves  of  the  superior  and  the  inferior  coronas ;  the  dew 
effect ;  the  fog  effect  and  shaking ;  the  fact  that  very  small  inferior 
coronas  are  followed  (ccet.  par.)  by  large  superior  coronas,  while  the 
latter  are  followed  by  large  inferior  coronas,  etc. 

e.  Finally,  while  superior  coronas  are  followed  by  inferior  coronas, 
and  vice  versa,  mean  coronas  follow  each  other. 

30.  Nucleation. — The  values  of  the  nucleation  (number  of  nuclei 
per  cubic  centimeter)  of  the  inferior  and  the  superior  coronas  naturally 
present  a  more  striking  contrast,  since  the  third  power  of  aperture  is 
involved.  Otherwise  but  few  new  results  are  to  be  inferred  from  them. 
If  the  long  series  of  table  10,  part  II,  be  taken,  which  contains  the 
data  of  twenty  successive  alternations,  the  average  inferior  nucleations 
are  11,800,  and  the  average  superior  nucleations  94,000,  supposing,  of 
course,  that  the  precipitated  water  is  the  same  in  both  cases  and  that 
it  is  all  condensed  on  the  available  nuclei.  In  other  words,  if  the  two 
cases  are  identical,  the  superior  coronas  correspond  to  a  number  of 
nuclei  8  times  greater  (frequently  larger  than  this  in  the  other  obser- 
vations) than  the  inferior  coronas.  As  this  explanation  is  the  more 
probable,  it  follows  that  the  nuclei  can  not  be  regarded  as  positive  and 
negative  ions.  They  are  rather  the  groups  of  large  and  small  nuclei 


32         NUCXEATION   OF   THE   UNCONTAMINATED  ATMOSPHERE. 

seen  throughout  the  condensations  in  connection  with  the  rain  and 
blurred  coronas.  Apart  from  this,  the  numbers  obtained  throughout 
are  quite  out  of  keeping  with  any  similarly  observed  ionizations.  If, 
however,  free  electrons  appear  only  at  the  destruction  or  at  the  origin 
of  nuclei,  the  association  of  few  ions  with  many  nuclei  at  any  time 
subsequent  to  their  origin  is  well  accounted  for,  as  already  suggested 
in  the  earlier  paper.  It  is  only  while  the  nuclei  are  being  produced 
that  the  ionization  and  the  nucleation  must  be  of  the  same  order ;  for 
the  latter  persists  while  the  former  vanishes  at  once.  Finally  the  fol- 
lowing results  are  implied,  at  least  for  the  physical  structure  of  air 
saturated  with  water  vapor  : 

Air  (dust-free)  is  inseparably  intermixed  with  large  and  small  nuclei, 
whose  number  (to  be  reckoned  in  millions  per  cubic  centimeter)  rap- 
idly increases  as  the  order  of  molecular  size  is  approached.  There 
seems  to  be  no  objection  to  looking  upon  these  nuclei  as  a  kind  of 
colloidal  (air)  molecule,  particularly  as  such  molecules  are  frequently 
producible  by  the  means  (Bredig)  which  produce  nuclei.  If  a  large 
number  of  free  atoms  is  suddenly  introduced  into  any  region  (and  this 
is  probably  what  the  radiation  of  the  above  kind  virtually  does)  the 
result  is  not  merely  a  production  of  typical  molecules  but  of  a  large 
concomitant  of  graded  nuclei. 

Practically  any  given  nuclear  status  of  air  is  a  counterpart  of  the 
intensity  of  the  ionization  of  the  medium  in  which  the  nucleation 
originated,  to  the  effect  that  the  superior  limit  of  size  of  the  nuclei 
and  their  number  increase  with  the  ionization.  But  there  is  no  case 
of  ionization  free  from  nucleation,  be  the  exciting  cause  a  mere  radi- 
ation as  above,  or  ignition,  combustion  (including  the  low-tempera- 
ture cases  like  phosphorus),  or  high  potential  discharge,  or  violent 
comminution  as  in  the  case  of  water  nuclei. 

EXPERIMENTS  WITH  DUST-FREE  AIR  ENERGIZED  BY  RADIUM. 

31.  Effect  of  radium  in  hermetically  sealed  glass  tubes.— A  modi- 
fication was  now  introduced  by  inserting  a  small  vial  of  thin  glass 
(walls  0.04  cm.)  containing  about  o.oi  gram  of  impure  radium 
(strength  io,oooX)  in  the  B  end  of  the  rectangular  apparatus,  Chap- 
ter I,  figure  i.  For  clearer  vision,  the  eye  at  the  goniometer  was 
placed  at  about  35  cm.  from  the  nearer  glass  plate  of  the  fog  chamber, 
and  the  apertures  so  obtained,  larger  than  the  customary  values  by 
about  10  per  cent,  appropriately  corrected.  The  data  of  most  of  the 
tables  are  reproduced  in  the  chart  containing  figures  26-32. 

The  filtered  air  was  first  examined  without  interference,  as  in  table 
1 8,  in  the  complete  absence  of  radium,  and  a  similar  test  precedes  all 
the  subsequent  observations.  The  results  for  air  are  without  perio- 


AIR    ENERGIZED   BY   RADIUM. 


33 


dicity  here  (figs .  27,28),  and  show  a  high  fog  limit  at  about  8p  =  24  cm . , 
the  coronas  at  8^  =  2^.7  being  just  appreciable.  The  reason  for  the 
raised  fog  limit  (air  freer  from  dust)  is  not  apparent ;  but  the  volume 
ratio  of  fog  and  vacuum  chambers  is  here  8/>  =  0.13. 

The  immediate  effect  of  introducing  radium  is  seen  in  the  second 
part  of  the  table,  at  first  without  periodicity,  and  the  fog  limit  is  at 
once  reduced  to  Bp  =  ig  cm.  (figs.  27,  28). 

TABLE  18. — Effect  of  radium  immediately  after  insertion.  Long  condensation  cham- 
ber. z/=n,ooocm.3;  z//F=o.i3.  Temperature,  26°  C.  Plug  valve.  Goniometer 
close  to  apparatus. 


Filtered  air  without  radium. 

Radium  tube  inserted. 

Ijft, 

s. 

A^X  io~3 

« 

5. 

^O- 

* 

, 

,000- 

2O.6 
21-5 

23-4 
23.2 
24.7 
24.7 
29.5 

29.6 
29.8 

33.1 

33-0 

0.0 

o.o 
o.o 
o.o 

1.5 
3.2 

3-5 
3-4 
3-5 
3-4 

o 
o 

0 

o 
2.7 
2.4 

20 
27 
25 
32 
27 

29-5 
26.9 
24.4 

22.  0 
20.1 

18.0 
18.0 

4.8 

3-9 
3-6 
2-5 
1-3 

o.o 

0.0 

75 
33 

24 
7 

2 
0 
0 

*24.8 

24.8 
24.8 
24.8 
24.8 
24.8 
24.8 
24.8 
24.8 
24.8 

6.0 

5-3 

2.8 

5-5 

4!s 
2.3 

5-4 

2.8 

74 
9.6 
70 
6.9 

58 
8.7 

3-5 
55 
6.8 

After  75  min. 

18.0 
20.  i 

21.6 

23.3 

24.8 
24.8 
24.8 
24.8 

o.o 

1.7 

3-8 

2.6 

5.2 
3.0 
5.3 

3-0 

O 
2 
25 

8 
73 
13 
76 

13 

After  about  90  min. 

24.8 
24.8 

5-4 
2.4 

55 
4-3 

After  1  8  hours. 

24.8 

*J6.2 
(2-7 

fioo 
6.8 

After  135  min. 

24.8 

6.0 

in 

*  Periodicity. 


t7V=i50,ooo;  ratio  1.5=  N\n. 


Nucleation,  75  minutes  after  the  first  observations,  has  much  in- 
creased (ccet.  par.)]  but  direct  comparison  is  not  possible,  because 
the  latter  data  are  now  distinctly  periodic,  and  an  upper  and  a  lower 
curve  of  apertures  has  appeared,  without  appreciably  displacing  the 
fog  limit.  After  further  135  minutes,  the  upper  limit  has  probably 
reached  a  stationary  value  (figs.  27,  28). 

In  the  last  part  of  the  table  the  periodicity  of  aperture,  s,  for  air  in 
the  presence  of  radium,  is  specially  investigated  for8/>  =  24.8  cm. 
Exceptionally  high  superior  values  of  ^  are  again  followed  by  excep- 
tionally high  inferior  values  (fig.  26),  while  exceptionally  low  inferior 


34        NUCLEATION  OF  THE  UNCONTAMINATED  ATMOSPHERE. 

values  are  followed  by  high  superior  values.  The  oscillatory  curves 
usually  riseifrom  great  depth  to  great  height.  The  s-curves  sometimes 
show  a  tendency  to  double  inflection  after  8p  =  24  cm.  is  exceeded,  ref- 
erable, it  would  seem,  to  the  normal  air  ions  added  to  the  radium  ions. 


.-£W 


FIG.  26. — Number  of  efficient  nuclei  (n)  obtained  in  successive  exhaustions  of  dust- 
free  air  energized  by  radium.  Periodicity. 

FIGS.  27-30. — Change  of  apertures  (s)  of  coronas  and  nucleations  (n)  varying  with 
the  pressure  differences  ($/)  in  cases  of  dust-free  air  energized  or  not  by 
radium  (in  sealed  glass).  Arrows  show  the  march  of  the  observations. 
Periodicity  is  apparent. 

FIGS.  31-32. — Decay  of  nuclei  produced  by  radium  after  removal  of  tube  from  fog 
chamber.  Radium  in  glass  tube. 

Table  9,  referred  to  in  figs.  26,  27,  and  28,  will  be  found  as  table  18,  p.  33. 
Table  10,  referred  to  in  figs.  29,  30,  31,  and  32,  will  be  found  as  table  19,  p.  35. 


AIR    ENERGIZED   BY   RADIUM. 


35 


In  table  19  the  same  effects  are  studied  after  the  radium  was  in  the 
apparatus  for  over  24  hours.  The  data  in  the  outgoing  series  (8/> 
increasing)  are  distinctly  periodic,  until  the  highest  value  8/>— 28.1  cm. 
is  reached,  which  seems  to  wipe  out  the  periodicity  for  the  returning 
series  (figs.  29,  30).  Curiously  enough,  the  fog  limit  has  apparently 
risen,  being  now  8  p  =  20  cm.,  instead  of  1 9,  as  in  table  18.  If  all  results 
be  compared  at  about  8p=  25  for  mean  values  of  s,  they  show  for — 


Air  (no  exposure),  5  =  1.4 

Radium,  short  exposure,  3.6 

exposure,  2  hours,  4.1 

exposure,  24  hours,  4.5 

Air  (20  minutes  after  removing  radium),   1.4 


(no  periods) 

(periods,  5  =  30  —  52) 

(periods,          27  —  62) 


=  1.7 
16 
23 
32 


Long  exposure  to  radium  has  increased  the  amplitude  of  the  variation 
of  aperture,  s.  The  limiting  maxima  for  high  values  of  §p  in  the 
case  of  radium  are  in  excess  of  the  corresponding  values  for  air. 


TABLE  19. — Effect  of  radium  left   in  apparatus  24  hours    (23°  C.) 

removed. 


and  thereafter 


Radium  present. 

Radium  removed. 

»/. 

s. 

A^Xio-3. 

Time. 

»>, 

5. 

^Xio-3. 

Mm. 

16.0 

O*O 

Q 

Q 

Removed 

18.0 

o.o 

O 

I 

21.7 

1.9 

3 

20.1 

Just  seen. 

o 

3 

21.7 

i.i 

2 

*21.7 

4-3 

34 

5 

21.7 

0.0 

0 

21.7 

i-7 

2 

10 

23-3 

1.0 

I 

24.8 

6.2 

116 

12 

23-3 

rf 

r' 

24.8 

2.7 

10 

15 

25.0 

o.o 

o 

fa8.i 

5-5 

101 

V? 

24.8 

*r' 

rf 

28.1 

5-1 

81 

20 

24.8 

x-7 

3 

28.1 

4.0 

37 

22 

24.8 

r' 

rr 

{24.8 

4.4 

43 

25 

24.8 

1.6 

3 

24.8 

4.8 

60 

28 

24.8 

i-3 

2 

21.7 

2.O 

3 

21.7 

2.Q 

10 

21.7 

2.9 

10 

*  Periodicity  even  in  the  absence  of  coronas.         f  Periodicity  ceases.         \  Returning. 

32.  Remarks  on  the  tables.— The  inference  has  already  been  drawn 
that  the  number  of  nuclei  as  well  as  their  size  varies  as  the  ionization 
per  cubic  centimeter.  The  fog  limit  is  reduced  by  the  presence  of 
weak  radium  in  sealed  thin  glass  tubes  within  the  chamber,  from 
8/>  =  24  to  19  cm.,  observations  which  may  be  made  pretty  sharply. 
This  implies  (quite  apart  from  number)  that  the  nuclei  in  the  pres- 
ence of  radium  are  larger,  as  they  are  the  offspring  of  a  more  highly 
ionized  field  than  exists  in  nonenergized  identically  filtered  air.  But 
apart  from  the  fog  limit,  the  number  of  nuclei  large  enough  to  fall 
within  the  scope  of  any  given  8p  is  correspondingly  increased. 


36        NUCLEATION  OF  THE  UNCONTAMINATED  ATMOSPHERE. 


The  fog  limit  of  filtered  air  after  the  radium  is  withdrawn  soon 
regains  its  original  value ;  but  some  definite  time  (say  1 5  minutes)  is 
necessary  even  here.  It  does  not  seem  to  vary  appreciably  with  the 
time  of  exposure.  (See  figs.  31,  32.) 

As  the  radium  of  low  power  (io,oooX)  is  inclosed  in  glass  0.04 
cm.  thick,  it  is  probable  that  ft  and  y  rays  are  chiefly  responsible  for 
the  nucleation.  Hence  it  appears  that  nuclei  are  produced  by  suffi- 
ciently swift  moving  corpuscles  as  well  as  by  the  X-rays,  an  important 
result  bearing  on  an  inquiry  suggested  above.  This  will  be  further 
substantiated  in  the  next  chapter  in  favor  of  the  gamma  rays. 


FIGS.  33-34. — Apertures 
of  coronas  (s)  and  nuclea- 
tions  (n)  varying  with  the 
pressure  differences  (8p), 
for  the  case  of  dust-free 
air  energized  by  radium 
acting  from  different  dis- 
tances. 

FIGS.  35-37.  —  D  e  c  a  y 
curves  found  after  the  re- 
moval of  the  radium  from 
the  fog  chamber. 

Table  u,  referred  to  in  fig. 
33,  will  be  found  as  table  20, 
P-  37. 

Table  12,  referred  to  in  fig. 
35,  will  be  found  as  table  21, 
P.  38. 

Table  i2a,  referred  to  in  fig. 
37,  will  be  found  as  table  22, 
p.  40. 


33.  Data  for  nucleation.— The  results  for  nucleation  in  case  of  a 
dust-free  atmosphere  energized  by  radium  (io,oooX)  contained  in  a 
hermetically  sealed  glass  tube  are  clearest  in  the  third  part  of  table 
1 8,  where  nearly  straight  w-curves  for  inferior  and  superior  coronas 
may  be  made  out  (fig.  28).  Part  2,  containing  data  obtained  shortly 


AIR    ENERGIZED   BY   RADIUM. 


37 


after  the  radium  tube  was  introduced,  is  not  easily  interpreted,  but  the 
action  of  radium  is  obviously  weaker.  In  most  cases  there  is  marked 
periodicity,  and  part  4  of  the  table  proves  that  the  nucleation  is  over 
9  times  greater  for  the  superior  than  for  the  inferior  coronas.  After 
an  exposure  of  18  hours,  the  nucleation  of  the  superior  coronas  is 
fully  20  times  greater. 

In  table  19  the  nucleations  of  the  superior  and  the  inferior  coronas 
are  particularly  striking  at  Sp  =  25.8,  and  the  ratio  is  actually  n 
(fig.  30).  Thereafter  periodicity  vanishes  with  falling  nucleations  and 
the  return  w -curve  is  along  an  average  path.  If  periods  were  due  to 
the  gradual  growth  of  nuclei,  supposing  that  the  time  between  two 
successive  exhaustions  is  needed  to  bring  the  nuclei  within  the  scope 
of  the  given  pressure  difference,  there  would  be  no  reason  for  the  rela- 
tively unbroken  return.  Oscillation  appears  to  be  wiped  out  by  high 
pressure  differences  as  well  as  in  a  march  of  decreasing  values. 


TABLE  20. — Radium   at   different   distances  from   line  of  sight, 
exhaustions  usually  2  minutes. 


Interval  between 


Distance. 

«/. 

s. 

N  X  io-3. 

Distance. 

8p. 

5. 

NX  io-3. 

00 

24.2 

o.o 

o 

oo 

24-5 

0.0 

0 

24.2 

o.o 

o 

24.8 

I.O 

2 

24.8 

1.2 

2 

24.8 

i-3 

2 

200 

21.7 

t2.3 

4 

45 

24.2 

3-7 

27 

21.7 

1.6 

2 

24.2 

3-4 

19 

21.7 

o.o 

0 

21.7 

2.8 

9 

21.7 

o.o 

0 

21.7 

2-7 

9 

21.7 

2.0 

3 

20.  i 

o.o 

o 

21.7 

1.8 

3 

20.3 

o.o 

o 

45 

20.8 

2.1 

4 

21.4 

i.i 

2 

20.8 

2.O 

3 

21.4 

I.O 

2 

20.  1 

O.O 

0 

20.3 

0.8 

i 

23-3 

1.8 

3 

100 

f  21.7 
\    21.7 
I   21.7 
(  21.7 
•J   21.7 

*2.2 
I.O 
2.2 
*(2.5) 

1.6 

4 

2 

4 
7 

2 

23-3 

24.8 
24.8 

2.0 

1.9 
2.1 

3 

4 
4 

(    21.7 

2.1 

4 

20.8 

O.O 

0 

24.8 

f2.2 

5 

20.8 

0.8 

8 

24.8 

2.1 

4 

*  Periods?.  f  After  40  minutes'  exposure. 

34.  Fog  limits  raised  by  weaker  ionization.— The  view  taken  in  this 
paper  that  the  size  of  the  nucleus  increases  with  the  intensity  of  the 
ionization  may  be  tested  by  removing  the  radium  from  the  apparatus 
and  allowing  it  to  act  from  increasing  distances  (figs.  33,  34).  This  is 
the  case  in  table  20,  where  observations  to  determine  the  fog  limit  are 


38         NUCLEATION   OF  THE  UNCONTAMINATED  ATMOSPHERE. 


given  when  the  radium  is  placed  at  45  cm.,  100  cm.,  200  cm.,  respec- 
tively, from  the  end  of  the  fog  chamber,  or,  better,  from  the  line  of 
sight.  Whenever  radium  is  not  too  far  from  the  apparatus  the 
change  of  fog  limit  may  be  made  out  sharply  as — 

Distance,  o  45  100  200  o°  cm., 

d£=  19  20.2  20-8  21.5          24.5         cm., 

showing  that  the  nuclei  increase  in  size  with  the  intensity  of  the  ion- 
ization.  These  and  the  following  data  are  mapped  out  in  figure  34  of 
the  chart,  n  instead  of  N  (reduced  to  normal  pressure)  being  usually 
inserted.  In  case  of  long  distances  (200  cm.)  the  results  are  apt  to 
be  irregular.  On  removing  the  radium  to  a  great  distance  the  fog 
limit  of  air  is  soon  restored,  and  it  will  be  seen  that  all  observations 
are  introduced  by  test  experiments  with  dust-free  air. 

TABLE  21. — Coronas  for  a  given  pressure  difference  and  fog  limits  after  removal  of 
radium  (o.oi  gram,  10,000  X,  in  hermetically  sealed  aluminum  tube)  from  inside  of 
fog  chamber. 


Time. 

it. 

Si,       S%. 

Fog  limit. 

WlXio-«"2 

h. 

o 

*2I.J 

4.8 

19 

36 

o 

*ig.o 

1.2 

2.1 

O.I 

t21.7 

4.0 

2O 

0.3 

21.7 

4.0 

2O 

0.7 

21.7 

4.0 

2O 

3-5 

£21.7 

3-7     3-0 

21 

17        8.0 

20.  0 

o.o 

o 

21.5 

$21.7 
$21.7 

2.6      2.2 
2.2      0.8 

22 

5-6     4-0 
3.0     0.8 

29-5 

21.7 

I.O      O.O 

23 

I.I      0.0 

24.7 

1.2 

1.4 

*  Radium  present.  f  Radium  removed.  \  Successive  exhaustions. 

35.  Nucleation. — An  important  interpretation  of  the  preceding  results 
is  obtained  by  mapping  out  the  nucleations,  n,  in  relation  to  the  cor- 
responding pressure  differences,  S/>  (fig.  34).  The  slope  of  these 
curves  falls  off  rapidly  for  radium  at  o,  45,  200  cm.  from  the  fog  cham- 
ber, while  the  fog  limit  rises.  In  other  words,  the  initial  slope  of 
the  « -curves  is  steeper  as  the  fog  limit  is  lower.  Thus  per  increment 
of  §p  of  i  cm.  of  mercury,  above  the  fog  limit  of  the  ionized  medium, 
and  below  the  fog  limit  of  nonenergized  dust-free  air,  there  will  be 
found  in  succession  for  radium  in — 

Sealed  aluminum  tube  within  fog  chamber,  5w=i2,ooo 

Sealed  glass  tube  within  fog  chamber,  6,000 

Sealed  glass  tube,  outside,  45  cm.  from  fog  chamber,  3,500 

Sealed  glass  tube,  outside,  200  cm.  from  fog  chamber,          1,000 
Dust-free  air  (above  fog  limit,  radium  at  infinity),  10,000 


AIR    ENERGIZED   BY   RADIUM.  39 

Hence  the  gradation  is  effectively  more  even,  finer,  /.  <?.,  with  fewer 
gaps,  as  the  fog  limit  is  low  and  the  maximum  size  of  nucleus  larger, 
while  for  sparse  distribution  the  steps  from  any  nucleus  to  the  next  in 
order  of  size  are  relatively  large.  For  a  different  medium,  dust-free 
air,  for  instance,  as  given  in  the  summary,  or  figure  34,  the  gradation 
is  characteristically  different.  L,ater  experiments  (Chapter  III)  make 
it  probable  that  the  curves  for  dust-free  air,  not  energized,  and  dust- 
free  air  energized  by  radium  and  X-rays,  make  a  continuous  series. 

36.  Radium  in  sealed  aluminum  tube.— The  identical  sample  of 
radium  (o.oi  gram,  io,oooX)  was  now  removed  by  cutting  the  glass 
tube,  put  into  an  aluminum  tube  (walls  about  o.i  mm.  thick),  and 
again  hermetically  sealed.  This  tube  was  introduced  into  the  inside 
of  the  fog  chamber,  kept  in  place  15  minutes  or  more,  and  then 
removed  to  an  infinite  distance.  The  results  obtained  are  different 
from  the  preceding  case  of  the  same  radium  in  the  thin  glass  tube  ; 
for  whereas  the  fog  limit  of  dust-free  air  was  regained  15  minutes  after 
the  removal  of  the  glass  tube  (figs.  31  and  32),  it  took  at  least  30  hours 
to  restore  the  same  fog  limit  after  the  removal  of  the  aluminum  tube. 
Table  21  shows  the  results,  where  s1  and  sz  are  apertures  obtained  in 
successive  exhaustions  about  2  minutes  apart,  dust-free  air  being 
added  to  the  fog  chamber  in  the  interval  (fig.  35). 

The  successive  fog  limits  for  radium  sealed  in  the  thin  aluminum 
tube  are,  therefore,  in  centimeters  of  mercury  (fig.  36), 

Radium  in  place,  8^  =  19 

Radium  tube  removed: 

Fog  limit  3>£  hours  later  21 

21  22 

30  23 

provided  time  is  allowed  for  the  excited  activity  within  the  chamber 
to  saturate  the  air  with  nuclei  (cases  s^.  When  such  time  is  not 
allowed  as  in  the  succeeding  exhaustions  (cases  s2),  the  fog  limit  of 
dust-free  air  is  practically  regained  in  30  hours.  Something  like  an 
emanation  seems  here  to  escape  from  the  aluminum  tube  rapidly  and 
from  the  glass  tube  slowly,  in  spite  of  their  thickness,  relatively  speak- 
ing, and  induces  radio-activity  at  the  inner  walls  of  the  fog  chamber; 
or  possibly  this  induced  activity  is  a  kind  of  phosphorescence  produced 
by  the  impinging  ft  and  y  rays.  It  seems  probable  that  the  life  of 
the  excited  activity  may  be  prolonged  at  pleasure  within  limits,  by 
gradually  decreasing  the  walls  of  the  aluminum  tube  hermetically 
sealing  the  radium  excitor. 

The  loss  of  the  activity  shown  by  the  rise  of  the  fog  limits  in  the 
lapse  of  time  is  naturally  of  an  exponential  character  (fig.  36).  It 
rises  quickly  after  the  removal  of  the  radium  from  Bp=ig  to  about 


40        NUCXEATION   OF  THE  UNCONTAMINATED  ATMOSPHERE. 


8/»  =  2i,  after  which  the  true  exponential  march  due  to  the  excited 
activity  begins.  It  would  be  better  to  state  these  data  in  terms  of  the 
number  of  nuclei  produced  after  indefinite  exposure  (nuclear  satura- 
tion), the  number  to  be  found  by  a  given  sufficiently  high  pressure 
difference  below  the  fog  limit  of  dust-free  air.  But  the  observations 
of  table  21  are  scarcely  advanced  enough  for  this  purpose.  In  fact,  the 
irregularity  of  size  of  the  coronas  s1  obtained  at  the  given  pressure- 
difference,  8/>=2i.7,  is  worthy  of  remark.  The  curves  obtained  in 
the  second  exhaustion  (s2),  whereas  but  a  few  minutes  of  exposure  of 
the  air  to  the  excited  activity  are  in  question,  are  much  smoother. 
The  n -curves  do  not  suggest  any  further  comment. 

The  above  experiments  on  radio-activity,  induced  by  radium  con- 
tained in  a  closed  aluminum  tube  placed  within  the  fog  chamber, 
having  been  made  soon  after  the  tube  was  filled  and  sealed,  it  was 
thought  necessary  to  repeat  the  work  two  months  later  with  the  same 
tube.  As  a  safeguard  this  was  additionally  sealed  at  the  ground  joint 
(screw  plug)  with  resinous  cement.  Data  so  obtained  with  the  wood 
fog  chamber  were  curiously  irregular,  showing  periodicity  occurring 
in  triads.  Large  coronas  appeared  after  long  waiting  (15  hours),  and  it 
is  therefore  probable  that  there  was  some  slight  leak  whereby  air  nuclei 
entered  the  fog  chamber  and  captured  much  of  the  precipitated  water. 
In  contrast  with  these  suspicious  results,  the  data  for  decay  curves  were 
consistent,  showing  an  increase  of  nucleation  within  about  20  to  30 
minutes  subsequent  to  removal,  after  which  a  gradual  decay  occurred 
to  about  one-half  in  6  hours.  But  the  data  as  a  whole  were  discarded. 

The  experiments  were  now  repeated  in  the  glass  fog  chamber,  which 
had  been  specially  tested  for  freedom  from  leaks.  The  exhaustions 
made  below  the  fog  limit  for  dust-free  air  are  shown  in  table  22  and 
figure  37. 


TABLE  22. — Radium  in  fog  chamber.    Sealed  aluminum  tube, 
sive  exhaustions,  im-2m  apart. 


cm.     Succes- 


Exh.  No. 

5. 

^X  io~3 

Exh.  No. 

5. 

NX  io~3 

Exh.  No. 

5. 

NX  io~3 

i 

4-5 

48.0 

9 

4.4 

44.0 

16 

2-3 

5-4 

2 

2.6 

Q.2 

10 

2.2 

5-0 

*7 

2-5 

8.0 

3 

I.O 

1.8 

ii 

.0 

.0 

18 

2.7 

10.4 

4 

*5-o 

67.0 

12 

3-4 

20.4 

19 

4.0 

32-4 

5 

2.7 

10.4 

13 

3-3 

18.6 

20 

t5-2 

74-4 

6 

I.O 

1.8 

J4 

*3-8 

30.0 

21 

3-7 

28.6 

7 

4.4 

44.0 

15 

*2.0 

3-8 

22 

3-7 

27.6 

8 

2.2 

5-o 

*  Renewed  after  waiting  5  minutes  or  more. 


t  Next  day. 


AIR   ENERGIZED   BY   X-RAYS.  41 

The  new  data  are,  in  fact,  quite  different  from  the  old.  After  intro- 
ducing the  sealed  radium  tube  the  nucleation  rises  rapidly  to  a  maxi- 
mum, falling  off,  however,  to  a  mean  value  in  14  hours.  On  removing 
the  radium  tube  from  the  chamber,  the  nucleation  falls  off  at  once  to 
about  10  per  cent  of  its  original  value.  This  appreciably  increases  a 
little  at  first,  but  vanishes  practically  in  the  ensuing  12  hours.  One 
may  note  that  the  second  and  subsequent  exhaustion  usually  show 
smaller  nucleations  than  the 'first,  as  though  it  were  possible  to  reduce 
the  nucleation  faster  than  it  is  restored.  It  is  probable  therefore  that 
in  the  first  experiments  something  like  an  emanation  escaped  from  the 
ground  joint  or  that  the  outside  of  the  aluminum  tube  had  become 
radio-active  during  filling.  Nevertheless,  a  residual  effect  is  in  evidence 
in  the  last  experiments  made,  which  can  not  be  explained  away. 
Something  has  escaped  through  the  aluminum  tube  which  produced 
the  lingering  radio-activity  of  the  chamber  (fig.  37). 


EXPERIMENTS  WITH  DUST-FREE  AIR  ENERGIZED  BY  THE  X-RAYS. 

3<T.  Persistence  of  nuclei  produced  by  X-rays  in  the  lapse  of  time.— The 

nuclei  produced  by  the  X-rays  of  sufficient  intensity  (z.  e. ,  when  the 
bulb  is  near  the  fog  chamber),  if  left  without  interference,  are  indefi- 
nitely persistent  as  compared  with  the  initial  ionization.  Table  23 
shows  some  incidental  results.  It  is  not  possible  to  determine  the 
law  of  decay  (probably  exponential)  by  this  method,  as  the  nuclei  are 
lost  or  otherwise  destroyed  by  the  condensation  which  determines  their 
number.  The  initial  nucleation  must  therefore  be  inferred.  Again, 
the  first  coronas  (if  the  X-ray  bulb  is  at  one  end  of  the  fog  chamber  as 
was  here  the  case)  are  apt  to  be  distorted,  so  that  the  corona  obtained 
on  first  exhaustion  is  not  available  for  definite  measurement.  To  some 
extent  the  datum  is  supplied  by  the  corona  of  the  second  exhaustion 
(s2),  observed  after  the  fog  particles  of  the  first  corona  (sj  have  sub- 
sided, filtered  air  slowly  replacing  the  exhausted  air.  m  refers  to 
the  precipitation  of  water  per  cubic  centimeter,  at  the  pressure 
differences  shown  by  the  subscripts. 

Within  an  hour  or  more  after  the  exposure  the  coronas  are  invari- 
ably strong.  Within  16  minutes,  36  minutes,  even  85  minutes,  they 
show  diminutions  of  aperture  comparable  with  that  usually  observed 
in  the  case  of  other  nuclei.  In  half  an  hour  the  nucleation  has  not 
fallen  below  ^ ,  in  an  hour  not  below  ^ ,  etc.  After  4  hours,  however, 
all  nuclei  within  the  scope  of  the  exhaustion  have  vanished. 


42         NUCLEATION   OF  THE   UNCONTAMINATED   ATMOSPHERE. 


TABLE  23. — Decay  of  X-ray  nucleation  in  lapse  of  time.     Exposure,  3  minutes; 
6  cells.     |  m^C^IIj'oo'  [    Goniometer  close  up. 


Time. 

5/. 

S'l.          *',. 

io~3X 
w'i              «'2 

io~3X 
n\            nz 

h.       m. 
16 

13-5 

6.9       3.0 

80               6.6 

66           5-4 
o              o 

V 

o 

36 

±oo 

13.5 
16.7 

16  7 

6.0-7.0  3.5 

4-7           1-5 
*Spindle  5  6 

68              ii 
28               1.4 

A     6 

56           9 
28            1.4 
46 

I      25 

J.U./ 

16.7 

3.8          1.2 

15                i.i 

15            LI 

*  Narrow  spindle  throughout  A  side. 

TABLE  24. — Fog  limits  obtained  with  X-ray  nuclei.  X-ray  bulb  at  different  distances. 
Exposure  for  different  times.  Line  of  sight  15  cm.  from  end  of  fog  chamber. 
Goniometer  close  up. 


J> 

6 

i 

g 

8 

a 

o 

X! 
0) 

£  % 

i 

^  .Q 

Remarks. 

*O   % 

§*! 

8$. 

5. 

i 

Remarks. 

'o  S 

n  8 

I* 

5. 

"o 

Q)     ^ 

rt  jfl 

M 

<u 

rt  2 

M 

g 

X 

s 

X 

H 

Q 

K 

H 

P 

Min. 

cm. 

^f«. 

cm. 

Current  on.... 

2. 

35 

18 

0.0 

o 

Current  on-. 

2 

2 

fi8.5 

4-5 

26 

off  • 

8 

T/r    _ 

off.... 

8 

•A 

1  / 

off.... 

*    e 

14.  y 

off 

i  .4 

-1'/ 

•"•DO 

25 

1.4 

7 

Current  on.. 

4 

2 

14.9 

5-3 

36 

on... 

•2. 

35 

24.8 

7.0 

110 

on.. 

4 

2 

II.9 

5-2 

28 

on... 

1 

35 

21.7 

5-0 

39 

on.. 

4 

2 

8.9 

O.O 

0 

on-  •• 

2, 

oe 

2O  I 

2  Q 

9       A 

Fofif  limit  •  • 

IO 

on... 

2 

35 

18.0 

O.O 

0 

off. 

TQ    e 

8 

10.5 

** 

off... 

"7  T    ^7 

±T7 

+  1/ 

off... 

O  3    3 

Fos   limit  «•• 

IO 

Current  on.... 

2 

10 

2O  I 

2n 

on.... 

18.5 



18 

*  Spontaneous  condensation  in  dust-free  air.         f  Distorted  coronas.        \  About. 

38.  Fog  limits  of  nuclei  produced  by  X-rays.— To  obtain  lower  fog 
limits  than  were  producible  with  the  weak  radium  above  employed, 
the  following  experiments  with  the  X-rays  (table  24)  were  undertaken. 
Bven  here  the  radiation  is  not  strong  (coil  with  4-inch  spark  gap  and 
energized  by  4  storage  cells). 


AIR    ENERGIZED    BY   X-RAYS. 


43 


The  following  fog  limits  were  made  out  with  the  aid  of  the  same 
fog  chamber  of  waxed  wood,  used  above  : 


X-ray  bulb 
from  chamber. 

Exposure. 

Fog  limit. 

35  cm. 
10 

2  min. 

2 

18 

10 
2 
2 
2 

4 

2 

4 

10 

15-5 

10 

Vanishing. 

A  few  other  cases  will  be  added  below,  giving  for  stronger  radiation 
at  a  distance  of  2  cm.  and  for  only  2 -minute  exposure  fog  limits  at 
5  and  4  cm.  In  each  case  the  air  was  rigorously  freed  from  dust  by 
filtration  before  the  exposure  began.  Hence  the  nuclei  are  due  to 
the  X-rays  alone,  and  their  size  increases  indefinitely  with  the  intensity 
of  the  ionized  field.  Indeed  as  to  size  they  eventually  in  no  wise  differ 
from  phosphorus  or  other  efficient  nuclei,  and  require  almost  no  super- 
saturation  to  induce  condensation. 


FIGS.  38-39. — Apertures  (s)  and  nucleations  (n)  varying  with  the  pressure  differences 

(8^)  for  the  case  of  persistent  nuclei  produced  in  dust-free  air  by  the  X-rays. 

Table  17,  referred  to  iu  figs.  38  and  39,  will  be  found  as  table  27,  p.  45. 

39.  Sudden  exhaustion  in  the  absence  of  condensation.— In  many  of 
the  experiments  the  nuclei  seemed  to  be  destroyed  by  sudden  exhaus- 
tion even  when  no  condensation  took  place,  the  pressure  differences 
lying  below  the  fog  limit.  As  this  is  an  important  question  bearing 
on  the  flying  to  pieces  of  the  nucleus,  special  investigations  were  made 
as  detailed  in  the  following  tables.  The  point  at  issue  may  be  stated 


44        NUCLEATION   OF  THE  UNCONTAMINATED   ATMOSPHERE. 


definitely  as  follows :  Let  8p  be  the  fog  limit  of  the  given  gas  satu- 
rated with  moisture.  Let  8/>'>  §p  be  a  pressure  difference  producing 
strong  coronas.  Let  §p"  <S/>  produce  no  condensation  at  all  in  the 
dust-free  gas  (below  the  fog  limit).  Then  if  the  fog  chamber  is 
exposed  to  radiation  in  a  definite  way,  in  a  definite  time,  and  thereafter 
left  without  interference,  §p'  will  produce  coronas  for  hours  after  the 
radiation  ceases.  If,  however,  immediately  after  the  exposure  §p"  is 
applied,  producing  no  condensation,  and  if  (dust-free  air  being  intro- 
duced at  once),  without  loss  of  time,  §p'  is  now  applied,  will  coronas 
appear  or  will  they  not  appear  in  spite  of  the  excessive  exhaustion  ? 
In  other  words,  has  the  nucleus  returned  to  dust-free  air? 

Thus,  in  table  25,  experiment  i  shows  that  mere  lapse  of  time  has  no 
relatively  important  effect.  In  experiments  2  and  3,  the  first  exhaus- 
tion at  8/>  — 18  has  all  but  destroyed  the  corona,  for  8p  =  2$  subse- 
quently applied,  which  should,  by  experiment  3,  have  been  5  =  7.0  cm. 
Similar  remarks  apply  to  experiment  4.  Experiments  5  and  7  instance 
the  usual  case,  that  if  a  corona  is  produced  in  the  first  exhaustion,  there 
will  always  be  a  smaller  one  in  the  second  exhaustion.  These  are 
the  favorable  experiments ;  but  experiment  6  and  others  which  might 
be  added  show  that  the  effect  of  the  lower  exhaustion  does  not  disrupt 
the  nucleus  for  the  higher  exhaustion.  Thus  there  is  no  trustworthy 
evidence  for  the  flying  to  pieces  of  the  nucleus,  and,  in  fact,  the  next 
section  (table  27)  shows  that  X-ray  nuclei  sustain  high  sudden  exhaus- 
tions without  being  dissipated  or  failing  to  produce  condensation. 
The  difficulties  encountered  are  without  doubt  referable  to  the  vari- 
ability in  action  of  the  X-ray  bulb. 

TABLE  25. — Possible  rupture  of  the  nucleus. 


First  exhaustion. 

Second  exhaustion. 

Time 

elapsed. 

8p. 

*. 

a*. 

5. 

Mm. 





3 

20.  i 

3-7 

18 

0.0 

25 

*i-3 



25 

7.0 

6 

(t) 

2-3 

13-4 

2.6 

13-4 

6.0 

2-3 

13-4 

4.1 

6 

(t) 

2-3 

13-4 

4-5 

13-4 

5.8 

2-3 

13-4 

3-4 

^Spontaneous  condensation.  fThin  drifting  fog. 

Experiments  were  also  made  under  satisfactory  conditions  with  the 
bulb  at  80  cm.  (table  26).  But  the  nuclei  so  obtained  are  essentially 
fleeting  and  would  vanish  without  the  first  exhaustion . 


AIR   ENERGIZED   BY   X-RAYS. 


45 


TABLE  26. — Attempted  breaking  to  pieces  of  nuclei.  Bulb  axial  at  80  cm.  from  end. 
Exposure,  3  min.  Fog-limit  air,  5  =  1.0 1.5  at  5^  =  24.7;  with  X-rays  origi- 
nally :  5/1=24.8,  5  =  3.8.  Filter  with  wet-sponge  tube. 


5  pi. 

Si. 

5^2- 

52. 

^ViXio-3. 

A^Xio-3. 

24.8 

3-9 

24.8 

i-5 

30.0 

2.7 

22.1 

3-0 

22.1 

.0 

ii.  3 

.0 

19.7 

.8 

24.8 

1.8 

i.i 

3-i 

IQ.2 

.0 

24.8 

2.1 

.0 

4-3 

24.8 

3-6 

24.8 

.8 

24.7 

1.4 

19.2 

.0 

24.8 

I.O 

.0 

1.8 

I9.I 

.0 

24.8 

I-J 

.0 

2.7 

24.8 

*3-3 

24.8 

ti-5 

18.5 

2.7 

*  Exposure,  7  min  :  8^  =  24.8,  5  =  3.6. 

t  Accidental  influx  rapid  and  large  :  §^  =  24.8,  53  =  2.8,  54  =  2.4,  55  =  0.8. 

40.  X-ray  nuclei  at  different  high-pressure  differences.— The  follow- 
ing experiments  originated  in  a  somewhat  similar  purpose  to  the  pre- 
ceding section.  In  table  27,  Si  and  s2  show  the  apertures  of  the 
coronas  on  first  and  second  exhaustion,  filtered  air  being  added  in  the 
meantime,  after  an  exposure  to  relatively  weak  radiation.  The  aper- 
tures are  a  maximum  at  8^  =  15  —  17  cm.,  after  which  they  decrease 
faster  than  the  increased  precipitation  on  the  nuclei  warrants  (fig.  39). 
The  w-curves  and  the  ^-curves  with  increasing  8p  are  both  similar. 
As  the  final  fall  of  curve  depends  on  the  difference  of  the  opposed 
effects  of  larger  precipitation  and  greater  number  of  particles  within 
the  range  of  condensation,  the  very  small  nuclei  must  here  be  in 
absence. 

TABLE  27. — X-ray  nuclei  at  different  pressure  differences.     Distance  of  bulb  from 

apparatus,  3  cm. 


Interval  of  exposure,  5  min. 

Exposure,  3  min. 

* 

*', 

*> 

MX.O-3 

^lOX- 

* 

5', 

*># 

^ViXio-3 

A^Xio  i 

21.7 

3-0 

o.o 

12.5 

.0 

24.7 

8.0 

4.4 

180 

45 

19.0 

4.4 

2.1 

33-7 

3-4 

24.7 

8.0 

4.1 

180 

37 

16.7 

5-6 

4.0 

6l.9 

23.2 

33-1 

5.0 

2.7 

102 

15 

13-4 

6.0 

58.6 

19-5 

24.7 

8.0 

4.4 

175 

46 

8.9 

3-3 

3-3 

£•4 

7-4 

16.7 

(t) 

47 

6.0 

(*) 

2-3 

8.9 

(t) 

5-3 



28 

13-4 

5-5 

4.1 

46.4 

19-5 

4.0 

(t) 

5-7 



14 

16.7 

(t) 

46 

*  Thin  drifting  fog. 


f  Long  spindle. 


Floating  veil. 


46         NUCLEATION   OF  THE   UNCONTAMINATED  ATMOSPHERE. 

Corresponding  experiments  given  in  the  second  part  of  the  table 
were  therefore  made  with  more  powerful  radiation  (fig.  38).  Here 
there  is  a  regular  decrease  of  aperture  from  the  beginning  where  pres- 
sure differences  are  vanishing  to  the  end  where  they  are  very  high. 
The  nucleations  nevertheless  pass  through  a  determined  maximum  at 
about  Bp—i6  to  20  cm.  The  endeavor  was  made  to  guard  against 
variation  of  efficiency  of  the  X-ray  bulb  and  other  causes  by  repeated 
redetermination  of  the  fiducial  pressures.  The  fog  limit  of  dust-free 
air  is  §p  —  24.7  here.  Hence  it  is  noteworthy  that  the  computed  nucle- 
ation  decreases  at  the  highest  pressure  differences  in  spite  of  the  acces- 
sion of  air  nuclei  to  augment  the  number  of  X-ray  nuclei  present. 
The  figures  (38,  39)  show  the  changes  of  n;  but  the  reduction  to  N 
(nuclei  per  cubic  centimeter  at  normal  pressure)  adds  nothing  new  to 
the  results. 

To  determine  the  nucleations  for  the  high  exhaustions  is  precarious, 
because  the  efficiency  of  the  apparatus  in  producing  truly  adiabatic 
conditions  will  rapidly  grow  less,  and  because  the  data  needed  for  the 
vapor  pressure  of  water  20°  or  more  below  freezing  are  not  forthcom- 
ing. A  method  of  quadratic  extrapolation  had  to  be  used  in  the 
present  table.  Indeed,  with  the  possibility  of  temperatures  below 
freezing  even  after  the  condensation  of  the  water  vapor,  the  whole 
phenomenon  becomes  very  complicated.  Hence  the  values  of  N  in 
table  27  are  mere  estimates  for  values  of  §p  exceeding  20  cm. 

It  may  be  observed,  in  conclusion,  that  in  all  the  above  cases  the 
X-radiation  was  cut  off  some  minutes  before  the  exhaustion,  so  that 
persistent  nuclei  are  alone  in  question,  to  the  exclusion  of  the  fleeting 
nuclei  discussed  in  the  next  chapter. 


CHAPTER  III. 


CRITICAL  CONDITIONS  IN  THE  FORMATION  OF  IONS  AND 

OF  NUCLEI. 

The  present  chapter  is  a  close  continuation  of  the  last,  and  is  sepa- 
rated from  it  for  convenience  in  treatment.  Dust-free  air,  energized 
or  not  by  radiation,  is  always  in  question.  The  subject  considered  in 
the  earlier  paragraphs  is  a  comparison  of  fleeting  and  of  continuous 
nuclei  and  the  passage  of  one  form  into  the  other  either  by  increasing 
the  strength  or  quality  of  the  radiation ,  or  by  solution .  The  effect 
of  both  methods  in  changing  the  fleeting  into  the  persistent  form 
is  possibly  the  same.  Afterwards  the  inquiry  is  reversed  and  the 
radiation  itself  examined  in  terms  of  the  nucleation  produced.  It  is 
noteworthy  that  penetrating  radiation  is  a  powerful  nucleator. 

41.  Apparatus — X-ray  bulbs. — A  number  of  medium-sized  bulbs  of 
German  pattern,  about  10  cm.  in  diameter  with  an  anticathode  2  cm. 
in  diameter,  were  used.  The  differences  between  these  were  no  greater 
than  the  differences  between  the  same  bulb  after  varying  periods  of 
action.  The  table  summarizes  a  few  data.  There  seems  to  be  a 
voltage  at  which  the  nucleation  (N)  produced  is  a  maximum. 

TABLE  28. — Comparison  of  different  bulbs.  Pressure  difference  8^  =  25  cm.  X-ray 
bulb  200  cm.  from  fog  chamber.  Exposure,  3  sec.  Exhaustion  during  exposure. 
Bulbs  10  cm.  diameter.  Anticathode  2  cm.  diameter,  except  No.  2,  which  was 
smaller. 


Bulb. 

Bulb 
vacuum. 

Coronal 
aperture. 

Si. 

Nucleation. 
ATX  io~3. 

No  o  (used  above)  

Low 

5  o~6  o 

6o~no 

Hifrh 

87  fi 

o 

87  6 

,, 

o 

5« 

,, 

.0 

c-    S 

4  with  lead  plate  ;  0.14  cm.. 

i  « 

D'° 
3-8 

30.0 

The  radium  referred  to  was  a  weak  sample  (io,oooX),  o.oi  gram  of 
which  inclosed  in  a  hermetically  sealed  tube  of  thin  aluminum  (walls 
o.i  mm.  thick)  sufficed  for  the  experiments. 

47 


48 


NUCLEATION   OF  THE   UNCONTAMINATED   ATMOSPHERE. 


42.  Fog  chambers— Filters  with  saturator.— The  long  rectangular  fog 
chamber  (Chapter  II,  section  16)  of  capacity  ^=13,000  cc.,  having 
the  volume  ratio  v  IV=o.i3  to  the  volume  V  of  the  vacuum  chamber, 
was  largely  used.  It  is  often  difficult,  however,  to  keep  plate-glass 
windows  perfectly  tight.  Hence  the  cylindrical  fog  chamber  (length 
45  cm.,  diameter  12  cm.)  was  substituted  for  it,  in  which  case 
vlV=o.o6.  Both  the  former  and  the  latter  were  often  incased  in 
sheet  lead,  0.14  cm.  thick,  leaving  merely  an  open  strip  in  the  broad- 
sides for  observation  of  the  coronas. 


FIG.  40. — Filter  with  wet-sponge  tube  (saturator). 

In  view  of  the  difficulties  encountered  in  the  preceding  chapter,  the 
attempt  was  finally  made  to  counteract  the  effect  of  periodicity  by 
saturating  the  filtered  air  with  water  vapor  before  introducing  it  into 
the  fog  chamber.  To  do  this  the  U  tube,  figure  40,  filled  with  pieces 
of  wet  sponge  was  added  to  the  filter  F,  the  filtered  air  from  B  entering 
the  fog  chamber  very  slowly  by  way  of  the  stopcock  C.  This  innova- 
tion seemed  at  first  to  be  remarkably  successful,  as  the  results  of  table 
29  on  page  50  will  show.  Later,  however,  there  was  a  very  definite 
recurrence  of  periodicity,  the  true  cause  of  which  I  ultimately  traced 
to  the  inevitable  formation  of  water  nuclei.  In  addition  to  the  filter 
mentioned,  an  ordinary  dry-cotton  filter  and  a  Pasteur  filter  were  often 
used;  but  the  latter  was  soon  discarded,  as  it  gave  no  additional  free- 
dom from  dust  and  prolonged  the  time  of  filtration  inordinately. 

F 


•  F 

•  JE 

A 

X 

:? 

•  io 

42 


FIG.  41. — Rectangular  wood  fog  chamber  A,  with  screening  lead  plates  P  and  X-ray 

bulb  B,  exhaust  pipe  E,  and  filter  pipe  F. 
FIG.  42. — Cylindrical  glass  fog  chamber  A,  with  lead  case  L  and  bulb  B.     E  is  the 

exhaust  pipe,  F  the  filter  pipe,  £  the  plug  for  cleaning,  and  "w  the  window. 


FOG   CHAMBERS.  49 

43.  Notation. — As  above,  the  angular  diameters,  <£,  of  coronas  will 
be  given  in  terms  of  s,  where  3oXsin  <£/2=.?/2,  as  the  arms  of  the 
goniometer  are  30  cm.  long ;  usually  <£  — ^30,  nearly.  To  secure 
clearer  vision,  the  goniometer  was  moved  up  to  the  plate-glass  window, 
placing  the  eye  somewhat  over  30  cm.  off.  The  source  of  light,  how- 
ever, was  left  at  250  cm.  from  the  trough,  as  above,  and  a  correction 
applied  for  the  distances. 


HF 


44 
43 

FIG.  43.— Rectangular  fog  chamber  A,  with  lead  tube  T,  filter  pipe  F,  and  exhaust 

pipe  E. 
FIG.  44.— Cylindrical  fog  chamber  A,  with  lead  tube  P,  exhaust  pipe  E,  filter  pipe  F, 

and  plug/. 

In  the  tables,  n  usually  denotes  the  number  of  nuclei  per  cubic 
centimeter  of  the  exhausted  air,  N  the  number  per  cubic  centimeter  of 
the  air  at  normal  pressure  and  temperature..  In  successive  exhaus- 
tions, without  fresh  nucleation,  the  apertures  will  be  written  sl  s%  ss 

and  the  nucleations  corresponding  NI  N2  N% If,  however, 

fresh  nuclei  are  added,  or  if  the  exposure  to  the  radiation  is  con- 
tinuous, si  $i"  Si"  and  NI  NI"  NI"  are  usually  used.  The  difference 
of  pressure  in  centimeters  of  mercury  between  the  inside  and  the  out- 
side of  the  fog  chamber  (taken  at  76  cm.)  is  denoted  by  8/>.  Hence 
if  p*  is  the  vapor  pressure  of  water  vapor,  the  corresponding  volume 
expansion  is  (76— />')  /  (76— p'—§p).  D  denotes  the  distance  of  the 
source  of  radiations  (X-ray  bulb,  etc.)  from  the  end  of  the  fog  chamber 
nearest  it.  Sfa  usually  refers  to  the  fog  limit,  /.  e.,  the  pressure 
difference,  below  which  there  is  no  condensation  in  saturated  dust- 
free  air,  within  the  scope  of  measurements  made  by  aid  of  coronas.  L 
shows  the  time  elapsed  between  the  end  of  the  exposure  to  radiation 
and  the  condensation. 

EFFECT  OF  LARGE  PRESSURE  DIFFERENCES. 

44.  Nuclei  in  dust-free  air  not  energized.— In  table  29  periodicity  has 
been  all  but  wiped  out,  and  the  incoming  and  outgoing  series  lie  as 
nearly  on  a  curve  as  may  be  expected. 


50        NUCLEATION   OF  THE  UNCONTAMINATED  ATMOSPHERE. 

TABLE  29. — Fog  limit  and  effect  of  pressure  difference  for  combined  filter  and  wet- 
sponge  tube.     Dust-free  air,  not  energized. 


»* 

s. 

A^Xio-3 

l> 

5. 

TV^Xio-8 

»* 

5. 

A^X  io~3 

24.8 

2.3 

i-7 

2.1 
2.1 
2.1 
.O 
I.O 
I.4 
2.7 
2.2 

5.2 

3-o 

4-4 
4.4 

4-5 
.0 
1.8 

2-5 
ii.  i 

5-3 

2.2 
3-0 
3-1 

3-o 
3-o 
3-i 
3-1 

3-2 

3-2 

2.7 

5-3 
15-1 
18.0 
16.4 
18.4 
24.9 
24.9 
24.1 

21.2 
II.  I 

24.7 
23-3 

Paste 
25.0 

Cottc 
25-0 

9 

ur  filter 
1-5 

m  filter  c 
.8 

2.4 
.0 

dry. 
2.7 

Iry. 
1.4 

28.0 
29.7 

33-o 
38.0 
38.0 
33-8 
30.5 
27-3 

22.6 
24.2 

25-5 
26.4 

The  data  for  aperture,  s,  reach  a  limit  as  8/>  continually  increases; 
but  beyond  the  highest  pressure  difference  applied,  s  will  probably 
again  decrease.  -W  therefore  must  continually  increase  within  the 
limits  observed,  but  beyond  them  it  will  also  eventually  decrease 
(curves  45  and  46). 

Incidental  observations  show  the  relative  effect  of  a  cotton  filter 
without  the  sponge  tube  (D,  figs.  45  and  46)  and  of  the  Pasteur  filter,  P. 
The  former  is  apparently  more  efficient  in  its  nitrations  than  the  Pas- 
teur filter,  which  has  the  additional  disadvantage  of  being  too  slow 
for  purposes  of  the  present  kind  (period  of  influx  prolonged  over  10 
minutes). 

Curiously  the  fog  limit  of  dust-free  air  is  reduced  by  the  sponge 
tube,  lying  in  the  given  apparatus  below  8/  =  23  cm.  for  rain  and 
below  8/>=24  for  cloud.  Such  precipitations  therefore  cease  when 
the  volume  increase  on  expansion  in  the  two  cases  is  respectively 
below  1.45  or  just  below  1.48,  data  which  are  naturally  larger  than 
C.T.  R.Wilson's  (Phil.  Trans.  Royal  Soc.  1897,  vol.  189,  p.  265),  in  view 
of  the  differences  of  the  apparatus  employed.  The  reduced  fog  limit 
with  the  wet-sponge  tube  may  be  referable  to  increased  supersatura- 
tion,  but  there  is  probably  some  specific  cause  yet  to  be  investigated.* 
The  highest  nucleations  observed  lie  within  7V=  25,000,  which  is  very 
far  below  the  conditions  at  which  axial  colors  occur. 

The  following  chart  (figs.  45-51)  illustrates  tables  29,  32,  33,  34, 
35,  36.  "Exp."  refers  to  time  of  exposure  to  radiation;  "8/>,"  to 
lapse  of  time  after  radiation  ceases.  D  is  the  distance  of  the  ionizer 
(X-ray  bulb  or  radium  tube)  from  the  nearer  end  of  the  fog  chamber. 


*  It  will  be  shown  elsewhere  that  the  (very  stow)  rate  of  filtration  is  here  essentially 
in  question. 


EFFECT   OF   X-RAYS.  51 

&  p  is  the  pressure  difference  observed  after  exhaustion .  The  ordinates 
are  often  merely  distributive  or  show  the  number  of  an  observation  in 
a  series.  The  fog  chambers  are  wood  or  glass  as  specified. 

i     '     i  . 


In  the  above  chart  the  terms  tables  2,  5,  6,  7,  8,  9  refer  to  the  tables  in  text  now 
numbered  29,  32,  33,  34,  35,  36. 

45.  Dust-free  air  energized  by  the  X-rays  from  a  distance.— In  table 
30  data  are  given  for  the  case  of  dust-free  air  feebly  energized  by  the 
X-rays,  the  filter  having  the  same  sponge-tube  attachment.  I  was 
not  at  the  time  aware  of  the  rapid  decay  of  the  nuclei  or  ions  produced 
by  these  means,  and  about  one-half  minute  was  allowed  to  elapse  after 


52        NUCLEATION  OF  THE  UNCONTAMINATED  ATMOSPHERE. 


the  exposure  to  the  radiation  before  the  observation  was  taken.  The 
resulting  apertures  are  thus  reduced,  about  two-thirds  of  the  nuclea- 
tion  having  vanished  ;  but  they  are  otherwise  comparable  and  much 
smoother  than  in  the  absence  of  a  lapse  of  time,  Z,,  between  the  end 
of  the  exposure  and  the  condensation.  Two  successive  exhaustions 
are  often  made  for  the  same  exposure,  for  which  A^  and  JV2  are  the 
nucleations  reduced  to  air  at  normal  pressure. 

TABLE  30. — Fog  limit  and  effect  of  pressure  difference  for  combined  filter  and  wet- 
sponge  tube.  Dust-free  air  energized  by  X-rays.  Observation  after  lapse  of  about 
30  seconds. 


Part  I.  —  Bulb  80  cm.  from  end  of  fog 

Part  II.  —  Bulb  150  cm.  from  end  of  fog 

chamber;  exposure,  3  min. 

chamber;  lapse,  30  sec. 

SJ>. 

Si. 

ss. 

MXio-3 

A^Xio-3 

sp. 

Si. 

*fr 

MX  TO-3 

A^Xio-3 

20.9 

2.1 

3-6 

20.9 

ri.7 

t".5 

2-5 

2-3 

24.8 

4.0 

*2 

32.0 

3-8 

24.8 

3-9 

i-3 

29.6 

2-3 

28.9 

•3-3    O 

(t) 

3  i 

32 

38.7 

17.4 

23  2 

28.9 

•3-3    0 

3-7 

A     0 

33.0 

A7  2 

16  6 

2Q 

37-1 

4.0 

53-3 

37-1 

3'7 

3-0 

45-4 

21.7 

41.2 

3-7 

53-8 

41.2 

3-1 

3-2 

§30.4 

32.4 

O/'1 

33.1 

'/ 

4.1 



40'4 
49-3 



4-L.Z 

41.9 

•o 

3.2 



O/-4 
45-2 



28.9 

3-8 



35-8 



48.0 

2.8 

23.1 

24.8 

3-8 



30.0 



37-i 

3.3 



30.6 

20.9 

1.8 



2.6 



33-0 

3-5 



33-5 



19.2 

.0 



.0 



28.9 

3-8 

2.7 

35-8 

11.7 

19.7 

.8 



I.I 



24.8 

3-3 

r  i.o 

18.3 

1.8 

22.1 

3-o 

O 

"•3 

.O 

24.8 

**i.3 



2.4 



24.8 

ttS-4 



83-4 



24.8 

«3-8 



30.0 



*  Air  nuclei.  \  Nonenergized  air.  **  Lapse,  3  min.     \\  Lapse,  30  sec. 

t  Accidental  delay.    §  Same  as  air  not  energized.    \\  Lapse,  o  min. 

In  the  first  part  of  the  table  (curves  52,  53),  while  the  values  of  si 
and  52  reach  a  limit,  the  nucleations  A^x  and  N2  continually  increase 
and  are  about  N=  25,000  apart  throughout  the  whole  range  §p  =  2$ 
to  41  cm.  NI  shows  the  number  of  nuclei  left  in  dust-free  air  about 
half  a  minute  after  exposure  to  the  X-rays  ;  N%  presents  the  case  of 
dust-free  air. 

The  second  part  of  the  table  is  irregular.  The  mean  curves,  how- 
ever, preserve  the  same  relations  at  first,  the  nucleations  of  the  ener- 
gized air  being  25,000  in  excess.  Toward  the  end  of  the  curves  both 
the  energized  and  nonenergized  air  show  apparently  decreased  nuclea- 
tion,  while  the  former  falls  to  the  low  values  due  to  the  normal  air 
nuclei  alone.  The  X-ray  excess  has  been  quite  wiped  out  at  §/  =  41  cm. 


EFFECT   OF   X-RAYS. 


53 


At  the  end  of  the  table  the  preponderating  effect  of  lapse  of  time 
after  exposure  is  indicated.  All  excess  of  nuclei  is  gone  after  3  min- 
utes, while  the  original  excess  of  83,000  is  reduced  almost  two-thirds 
in  half  a  minute. 

46.  Continued — Rays  not  cut  off  during  condensation. — Table  31 
(curves  54,  55)  contains  data  for  the  coronal  apertures  obtained  without 
cutting  off  the  radiation  until  after  condensation  has  been  produced. 
The  two  minutes'  interval  of  exposure  is  excessive  (as  the  following 
paragraphs  show)  when  weak  radiation  (distance  of  X-ray  bulb  from 
end  of  fog  chamber,  D  =  150  cm. )  is  in  question.  The  results  in  table 
31  are  distributed  cyclically,  and  the  return  series  shows  less  nuclea- 
tion  in  general  than  the  outgoing  series.  This  is  attributable  to  the 
gradual  temporary  loss  of  efficiency  of  the  X-ray  bulb.  Similarly  the 
fog  limit  is  slightly  below  20  cm.  in  the  outgoing  series  and  slightly 
below  21  cm.  in  the  return  series,  the  rise  being  toward  the  nonener- 
gized  dust-free  air  (8^0  =  24  cm.). 

TABLE  31. — Fog  limit  and  effect  of  pressure  difference  for  combined  filter  and  wet- 
sponge  tube.  Dust-free  air  energized  by  X-rays.  Bulb  150  cm.  from  end  of  fog 
chamber.  Exposure,  2  min.  Observation  taken  during  exposure,  or  lapse,  o  sec. 


* 

Si. 

s 

2- 

AiXio-3 

JVaX 

io-« 

* 

s\. 

5 

2- 

AiXar- 

^Xxo- 

20.0 

r  i.o 

1-3 

45-4 

4-5 

... 

112 

21.7 

4.2 

32.5 

41.2 



1 

3 



36.3 

23-3 

4.6 

47-5 

37.1 

5-5 

I44.I 

24.8 

5-4 

82.2 

33-0 

92.7 

28.9 

6-3 

147.0 

28,9 

4.8 

71.7 

33-o 

5-5 

123.1 

24.8 

5-4 

82.3 

37-  1 

5.6 

151.3 

20.9 

1.8 

2.6 

41.2 

5.6 

179.4 

In  addition  to  this,  the  outgoing  and  the  return  series  show  a  curi- 
ous case  of  periodicity  which  may  or  may  not  be  real ;  but  it  is  prob- 
able that  there  is  decreased  nucleation  after  8/>  exceeds  40  cm.  The 
initial  increase  of  N  with  &p  is  nearly  straight  and  exceedingly  rapid 
(8^/8^  =  15,000,  nearly).  This  is  somewhat  greater  than  the  above 
values  for  radium  (about  12,000),  but  of  the  same  order  as  the  datum 
for  weak  X-ray  radiation.  The  corresponding  data  for  dust-free 
nonenergized  air,  given  in  the  same  chart,  show  that  initially 
8NI$p  =  5,000,  nearly,  in  correspondence  with  the  earlier  data  so  far  as 
can  be  made  out.  The  nucleations  N  are  throughout  small  as  com- 
pared with  energized  air,  the  excess  in  the  latter  case,  if  mean  values 
be  taken,  being  of  the  order  of  100,000  nuclei  per  cubic  centimeter. 


54         NUCLEATION  OF  THE  UNCONTAMINATED  ATMOSPHERE. 


60 


40 


£0 


2ft          24          26          28          30          K         54-          36          38 


26          30          34          38          42          44          20          «-          88          32,          36          40         44- 
FIGS.  52-55. — Illustrating  tables  30,  31. 

Tab.  3,  in  the  above  chart,  is  replaced  by  the  present  table  30  in  the  text ;  Tab.  4,  by  the  present 

table  31. 

GENERATION  AND  DECAY  OF  NUCLEI. 

4T.  Fleeting  nuclei. — This  brings  the  work  to  the  main  purposes  of 
the  present  paper,  viz,  to  compare  the  generation  and  decay  of  the 
nuclei  produced  by  the  X-rays  when  the  density  of  ionization  or  of 
electrification  has  different  values.  It  was  shown  conclusively  above 
that  with  strong  radiation  the  nuclei  persist  for  hours,  and  it  follows 
from  the  foregoing  paragraphs  that  for  weak  ionization  they  are  fleet- 
ing. Hence  there  must  be  transitional  conditions,  and  these  are  to  be 
investigated,  both  for  the  production  and  for  the  decay  of  nuclei. 

With  such  an  end  in  view  a  strong  X-ray  tube  may  be  placed  at 
different  distances  from  the  end  of  the  fog  chamber  and  the  results 
referred  to  the  nucleation  within,  or  the  same  bulb  in  the  efficient  and  the 
partially  fatigued  condition  may  be  placed  at  a  fixed  distance  near  the 
apparatus.  The  second  method  is  usually  inseparable  from  the  first. 


GENERATION   AND   DECAY. 


55 


Data  are  given  in  table  32  et  seg.,  the  pressure  difference  being 
chosen  at  the  fog  limit  of  dust-free  air,  which  under  these  conditions 
contributes  but  a  few  per  cent  of  the  nuclei.  The  first  part  of  table 
32  shows  that  the  origin  of  nuclei  is  practically  instantaneous.  Within 
5  seconds  after  the  radiation  from  the  X-ray  bulb  (placed  at  D  =  i$o 
cm.)  begins,  the  air  within  the  fog  chamber  is  saturated  with  nuclei 
(curve  47). 

Decay  is  not  quite  instantaneous,  but  enormously  rapid  as  compared 
with  the  care  for  intense  radiation  of  the  preceding  chapter.  The 
number  of  nuclei  per  cubic  centimeter  is  reduced  one-half  in  about 
2  seconds  and  reduced  one-fifth  in  20  seconds.  After  120  seconds  the 
nucleation  of  dust-free  air  is  practically  regained.  The  decay  is  not 
apparently  exponential  in  character.  If  N=N0e  ~at,  the  data  of 
tables  32  and  33  are  badly  reproduced.  With  N=N0j(i -\-V£)  or 
\\N=a-\-bt,  the  agreement  is  as  good  as  the  observations.  Hence 
—dn\dt  =  bri*,  or  the  decay  is  as  the  square  of  the  number,  showing  that 
the  destruction  is  mutual  between  the  nuclei  as  if  they  were  positive 
and  negative  ions. 

TABLE  32. — Generation  and  decay  of  the  nuclei.     X-radiation,  bulb  at  D  =  i$o  cm. 
d£  =  25  cm.     Filter  and  wet-sponge  tube. 


I.  Generation. 

II.  Decay. 

Time  of 
exposure. 

* 

jVXio-3 

Time  after 
exposure. 

s. 

^Xxo- 

Sec. 

Sec. 

*o 
30 

t'i 

*0 

r'i.5 
5-3 
5-5 
5-4 

I.O 

3-0 
79.0 
87.6 

83-4 
1.8 

10 

15 
15 
20 
20 

3-6 

3-7 
3.6 

3-4 
3-4 

25.0 

27.6 

25.0 

21.2 
21.2 

0 

5-6 

92.O 

30 

t2.0 

3-8 

II.  Decay. 

30 
30 

3-2 

13-2 

16.6 

16.6 

Time  after 

60 

2.6 

9.2 

exposure. 

5. 

^X  10 

60 

2.6 

9.2 

1  20 

2.2 

5*^ 

1  20 

2.1 

4.4 

Sec. 

o 

5-4 

83-4 

5 

3-8 

30.0 

0 

$4.8 

60.0 

5 

35.0 

0 

4.8 

60.0 

5 

4.0 

32.4 

5 

16.6 

10 

3-4 

21.2 

5 

4.0 

32.4 

*  Dust-free  air  not  energized. 

\  Note  the  low  apertures  after  full  corona. 


t  Nucleation  produced  instantly. 


56         NUCIvEATlON   OF  THE  UNCONTAMINATED  ATMOSPHERE. 
TABLE  33. — Continuation  of  the  preceding.      Bulb  at  40  cm.     $p  =  25  cm. 


I.  Generation. 

III.  Decay. 

Time  of 
exposure. 

5. 

*X«* 

Time  after 
exposure. 

S. 

^Xio- 

Sec. 

Sec. 

0 

ro.S 

I.4 

5 

3-8 

30.0 

60 

5-2 

74-4 

5 

4.0 

32.4 

15 

5-2 

74-4 

5 

3-7 

27.6 

5 

5-2 

74-4 

15 

3-4 

20.4 

o 

8.8 

1.6 

.... 

3-6 

25.0 

60 

2.7 

IO.O 

.... 

2.8 

II.  O 

II.  Fog  limit  at  20  cm. 

120 
30 

2.0 

3-3 

3.8 

18.6 

.... 

3-2 

16.6 

sp. 

•  s. 

NX*o-* 

0 

5-6 

92.0 

21.6 

3-0 

ii.  i 

20.  i 

I*5 

2.2 

18.4 

0.0 

.0 

*  Nucleation  produced  instantly. 
TABLE  34. — Continuation  of  the  preceding.     Bulb  at  io  cm, 


Time  of 
exposure. 

.. 

arx^ 

Time  aftei 
exposure. 

^Xzo- 

Time  of 
exposure 

,. 

ATX^ 

I.  Generation.    Sp  =  20.1. 
(Rays  on.) 

II.  Decay.     Exposure  60 

IV.  Generation.     d£  = 
24.8.     (Rays  on.) 

Sec. 

15 
60 

120 

5 
5 
15 
5 
5 
5 
30 
30 
60 
1  20 

2.1 

3-* 
3-4 
1.9 

2.O 
3-2 
1.2 
.0 
.0 
2.8 

2.3 

3-4 

3-4 
11.4 

15-9 

2.8 

?  12.9 

.0 

.0 
8.6 
4.2 
10.3 
15.9 

Sec. 
15 

10 

5 

0 

i-9 
2-3 

2-5 

4.2 
11.4 

Sec. 
5 

60 

5 
60 

4.0 

4-5 
4-5 
4-5 

4-7 

34-4 
48.0 
48.0 
48.0 
56.0 

^ 

5. 

A^Xzo- 

V.  Generation.      Sp  = 
20.  i. 

III.  Fog  limit,     i    min. 
exposure.     (Rays  on.) 
Fog  limit,  18  cm. 

Sec. 

15 
60 

120 

2.1 

3-4 

3-4 
11.4 

15-9 

20.1 

18.4 

21.6 

23-3 

24.8 

.8 
3-5 
3-9 
4-9 

11.4 
.8 
19.2 
28.5 
63.0 

DECAY   CONSTANTS — PERSISTENT  NUCLEI. 


57 


If  N  be  expressed  in  thousands  per  cubic  centimeter,  the  following 
is  a  summary  of  the  results  obtained : 


o  sec. 

20  sec. 

60  sec. 

( 

78 

IQ 

8 

First  series,  a  —  0.0128,  b—  0.0020...  \ 

78 

IQ 

go 

18 

Second  series,  #  =  0.0120,  6  =  0.00218-] 

80 

18 

7" 

The  effect  of  periodicity  is  still  in  evidence,  seeing  that  the  large 
coronas  are  apt  to  be  followed  by  relatively  small  coronas.  Some 
special  results  are  given  in  the  table.  The  coronas  at  these  distances 
are  round,  but  blurred,  showing  the  occurrence  of  nuclei  of  all  sizes. 

At  D  =  40  cm.  (table  33  and  curve  48),  the  results  are  not  essentially 
different.  The  X-ray  bulb  is  weak  at  first,  but  seems  to  recuperate  in 
the  course  of  the  work .  In  other  respects  the  two  curves  are  essentially 
the  same,  as  the  above  data  show.  In  spite  of  the  variability  of  the 
X-ray  bulb,  the  insignificant  differences  of  nucleation  in  these  two 
cases  are  astonishing,  for  the  distances  vary  from  40  to  150  cm.  The 
law  of  inverse  squares  would  predicate  a  fourteen-fold  decrease.  In 
fact,  the  same  anomalous  result  seems  to  hold  quite  up  to  the  fog  cham- 
ber, as  suggested  in  the  data  of  table  34, 

The  bulb  in  table  34  is  unfortunately  weaker,  showing  only  about 
half  the  nucleation  of  the  preceding  case  (^  =  48,000  at  8/>  =  24.8  cm., 
for  instance)  in  spite  of  greater  nearness  (Z?  =  iocm.).  The  earlier 
data  may  have  been  larger,  ^=63,000  being  among  these.  The  fog 
limit  has  been  definitely  reduced  from  20  cm.  to  18  cm. 

Generation  is  now  no  longer  instantaneous ;  certainly  not  at 
Sp  =  20.  i ,  though  the  data  at  the  larger  pressure  difference  Sp  =  25  are 
not  decisive.  It  takes  at  least  2  minutes  for  the  given  radiation  to 
saturate  the  air  with  nuclei  corresponding  to  Sp  =  20.  i .  (See  curve  51.) 

In  conformity  with  the  slow  generation  of  nuclei  the  period  of  decay 
is  now  definitely  prolonged.  In  3  to  4  minutes  the  nucleation  is 
reduced  one-half. 

48.  Persistent  nuclei.— The  data  for  stronger  radiation,  showing 
remarkably  persistent  nuclei  by  comparison ,  have  already  been  given 
in  Chapter  II,  section  37  et  seq.,  and  are  repeated  in  the  annexed 
curve  (50).  Roughly,  the  reduction  is  one-half  in  about  10  minutes 
and  four-fifths  in  80  minutes,  contrasting  sharply  with  the  reductions  in 
2  seconds  and  20  seconds,  respectively,  in  the  case  of  weak  ionization. 


58        NUCIvEATlON  OF  THE  UNCONTAMINATED  ATMOSPHERE. 
TABLE  35.  —Data  for  persistent  nuclei.     D  =  6  cm. 


Time  of 
exposure. 

Time 
after 
exposure. 

9* 

Si. 

s*. 

MXicr3. 

A^Xio-3. 

Min. 

h.     m. 

3 

o 

13-5 

*  7.0 

3-5 

86.0 

12.7 

o     16 

13-5 

6.9 

3-0 

82.9 

6.8 

4       o 

13-5 

.0 

.0 

.0 

3 

0 

16.7 

*Spindle. 

5-6 

(100) 

60.0 

36 

16.7 

4-7 

i-5 

36.4 

1.8 

i     25 

16.7 

3-8 

1.2 

19.5 

i-5 

*  Distorted. 

Assuming  the  above  equation  \\N=a+bt,  or  —  dN\dt  =  bN*i,  for 
which,  however,  there  is  no  immediate  justification  here  and  which 
does  not  fit  well,  values  of  the  order  of  a  —  o.oi  and  b  =  o.ooooi  follow. 
The  decay  is  thus  shown  to  be  several  hundred  times  slower  than 
above,  under  like  assumptions. 

In  table  36  and  curve  5 1  specific  results  for  the  generation  and  decay 
of  nuclei  have  been  added,  obtained  with  a  bulb  strong  at  first,  but 
eventually  losing  intensity  below  the  necessary  limit.  The  first  part 
of  the  table  shows  a  law  of  generation  increasing  with  the  time  of 
exposure  at  an  accelerated  rate,  consistently  throughout  the  180  sec- 
onds of  observation.  The  remaining  conditions  have  already  been 
investigated  in  Chapter  I .  Measurement  is  difficult  because  of  the 
distorted  coronas,  which  soon  become  densely  stratified  fogs.  The 
pressure  difference  used  (8p  =  2o  cm.)  is  below  the  fog  limit  for  air. 

The  curve  (51)  for  nucleation  (N)  shows  an  enormously  rapid 
increase  after  i  minute  of  exposure,  as  though  the  nuclei  themselves 
became  radio-active,  temporarily.  This  increase  is  sustained  even  if 
the  radiation  is  cut  off.  (Section  56.) 

The  results  for  decay,  in  case  of  the  persistent  nuclei  here  obtained, 
are  complicated  and  must  be  given  in  curves.  In  the  second  part  of 
the  table  the  minute  exposures  show  but  slight,  if  any,  decay,  in  the 
absence  of  radiation,  after  the  lapse  of  i  minute.  The  2-minute 
exposures  actually  seem  to  show  increased  nucleation  in  the  minute 
succeeding  exposure  (secondary  radiation,  section  16);  but  in  the 
ensuing  5  minutes  after  radiation,  decay  is  manifest  (curve  51).  The 
behavior  of  the  fatigued  X-ray  bulb  may  be  contrasted  with  this,  in 
the  same  position  (part  IV).  The  nuclei  vanish  as  in  the  third  part 
of  the  table,  in  spite  of  the  2-minute  exposures  as  compared  with  the 


PERSISTENT  NUCLEI. 


59 


i -minute  exposures  of  the  former  case;  and  these  inferences  are  cor- 
roborated by  the  last  observation  (part  V)  at  the  original  low 
8^  =  20  cm. 

TABLE  36. — Continuation  of  the  preceding.     Bulb  at  6  cm. 


Time  of 
exposure. 
(Rays  on.) 

Time  after 
exposure. 
(Rays  off.) 

I/. 

,: 

* 

«X^ 

—  -• 

I.  Generation. 


5  sec. 

o  sec. 

20.  i 

1.8 

2e 

10 

20 

Q 

O'1 

11.4 

60 

o 

.u 

•3    6 

1U.J 

180 

Strata  (Q  A) 

5e 

Ayo 

(coo) 

fi8    a 

60 

o 

•3    6 

O 

\:>w) 

I2O 

o 

Strata  (*  A] 

32 

•iyo 
(TOO) 

M 

iz.y 

II.  Decay. 


60 

2O  I 

32 

60 

T  e 

•* 
32 

iz.y 

60 

XJ 

OQ 

o  2 

iz.y 
12  O 

60 

6O 

*2*8 

(A  A) 

60 

I2O 

*3  o 

TO  a 

120 
I2O 

120 
300 



Strata  (6.0) 
tS-6 

3-5 
3-0 

(130) 
71.8 

I7.6 
10.3 

III.  Decay.     Larger  dp. 


60 

0 

24.8 

5-5 

87.6 

60 

60 

3-i 



14.6 



60 

0 



4-5 



48.0 



60 

o 



4-5 



48.0 



60 

60 



2.6 



9.2 



60 

60 



2.8 



II.  0 



IV.  Decay. 

120 

60 

24.8 

2.9 

n.8 

120 

0 

fc.0 



66.0 



Bulb    ) 
tested  f  I2° 

o 

20.  i 

fcM 



5-i 



*  Coronas  distorted  with  much  rain.      Heavy  fogs  near  bottom.      Coronas  more 
blurred  and  foggy  as  the  time  after  exposure  increases. 

f  Corona  after  5  minutes'  waiting,  round;  not  stratified,  but  blurred. 
\  Bulb  too  weak  for  strata.     lonization  density  below  entrance  valve. 


60        NUCLEATION   OF  THE  UNCONTAMINATED  ATMOSPHERE. 

A  comparison  of  the  i -minute  exposures  in  parts  II  and  III  is  note- 
worthy (curve  51).  The  high-pressure  difference  in  part  III  (S/>  =  25) 
catches  over  four  times  as  many  nuclei  as  the  low-pressure  difference 
(8^>  =  2o),  cat.  par.,  but  the  excess  vanishes  at  once  to  the  value  of 
those  within  the  reach  of  8p  =  20  cm.  Hence  evanescent  and  persist- 
ent nuclei  are  always  present  together. 

49.  Persistence  of  fleeting  nuclei  after  solution.— A  result  occurring 
throughout  the  observations  is  the  following :  Whether  the  nuclei  are 
fleeting  in  character  or  not,  there  is  invariably  a  second  strong  corona. 
This  is  obtainable  on  the  succeeding  exhaustion  without  fresh  nuclea- 
tion,  even  if  the  fog  particles  of  the  first  corona  are  allowed  to  com- 
pletely subside,  before  the  addition  of  the  dust-free  air  prior  to  the 
second  exhaustion.  If  there  were  no  first  exhaustion  during  the 
exposure  of  the  fog  chamber  to  the  radiation,  no  nucleation  would 
have  been  found  after  the  lapse  of  time  needed  preparatory  to  the 
second  exhaustion .  The  reevaporation  of  fog  particles  from  the  first 
exhaustion,  in  every  case  changes  about  one-eighth  of  the  fleeting  nuclei 
into  the  stable  nuclei  observed  in  the  second  corona.  This  is  obviously 
an  important  observation,  bearing  on  the  whole  phenomenon  of  nuclei, 
condensation  and  rain. 

To  investigate  this  case  the  data  of  table  37  were  collected,  in  which, 
as  soon  as  possible  after  first  condensation,  dust-free  air  is  admitted 
into  the  fog  chamber  to  dispel  the  fogs  by  evaporation.  When  this  is 
done  the  coronas  on  second  exhaustion  are  invariably  larger  and  denser 
(curves  56,  57),  showing  that  more  nuclei  have  been  preserved,  i.e., 
converted  from  the  fleeting  into  the  stable  form.  The  only  effect 
producible  by  the  premature  influx  is  to  diminish  the  number  of  fog 
particles  lost  by  subsidence.  It  follows,  then,  that  all  nuclei  upon 
which  condensation  has  once  taken  place  become  stable  nuclei. 

It  is  somewhat  difficult  to  measure  the  first  corona  and  at  the  same 
time  to  provide  for  a  quick  influx  of  air  so  that  but  little  subsidence 
of  fog  particles  may  take  place.  The  data  of  table  37,  therefore,  quite 
apart  from  periodicity  and  other  difficulties,  can  not  be  expected  to 
be  very  uniform.  It  was  not  thought  necessary  to  prolong  the  interval 
of  persistence  (time  from  influx  of  air  to  second  exhaustion)  beyond 
a  few  minutes,  for  these  suffice  to  indicate  persistence.  The  table 
shows  that  from  25  to  50  per  cent  of  the  nuclei  may  be  preserved 
indefinitely  by  reevaporating  them  from  fog  particles.  The  mean 
datum  of  all  results  apart  from  the  time  interval  entering  the  test  is 
actually  39  per  cent. 


PERSISTENCE    ON  SOLUTION. 


6l 


TABLE  37. — Showing  that  fleeting  nuclei  become  stable  on  solution.  Rectangular 
wooden  fog  chamber  in  lead  casket.  5^  =  25  cm.  Exposure  to  X-rays,  3  sec. 
Distance  of  X-ray  bulb,  200  cm.  Mere  rain  denoted  by  r. 


Time  elapsed 
after  expos- 
ure to  first 
exhaustion. 

Time  elapsed 
from  first  ex- 
haustion to 
influx. 

Time  elapsed 
from  influx 
to  second  ex- 
haustion. 

9f 

s, 

S3- 

«- 

«x,. 

Part  I. 


Sec. 

Sec. 

Sec. 

o 

o 

60 

4-7 

3-3 

*i-7 

56.0 

18.6 

o 

o 

60 

3-3 

i-7 

(49) 

18.6 

o 

o 

60 

(4.3) 

3-1 

r 

41.0 

14.6 

0 

o 

60 

3-8 

2.9 

r 

30.0 

n.8 

60 

60 

.... 

i-9 

r 

.... 

3-6 

.... 

60 

60 

i-7 

r 

.... 

3-0 

.... 

0 

o 

60 

4.4 

3-4 

r 

44.0 

20.4 

0 

0 

120 

3-8 

2.8 

r 

30.0 

10.4 

0 

0 

300 

4-7 

3-i 

r 

56.0 

14.6 

Part  II. 


0 

o 

60 

4-3 

3-2 

r 

41.0 

16.6 

0 

o 

60 

3-9 

2.9 

r 

31.2 

n.8 

0 

0 

60 

3-4 

2.6 

r 

20.4 

9.8 

Part  III. 

0 

o 

60 

4-5 

3-2 

r 

48.0 

16.6 

0 

o 

120 

3-7 

2.9 

.... 

27.6 

n.8 

o 

o 

60 

3-o 

2.5 

o 

13.2 

8.0 

o 

o 

120 

4-7 

3-o 

r 

56.0 

13.2 

Part  IV.  Cylindrical  glass  fog  chamber.     8^  =  22.     Z>=iocm. 


0 

O 

I2O 

5-o 

2.9 

r 

66.0 

11.8 

o 

O 

60 

5-7 

3-4 

r 

96.4 

20.4 

0 

O 

180 

5-2 

3-0 

r 

74-4 

13-2 

60 

60 

.... 

2.0 

r 

.... 

3-8 

1.8 

120 

60 

I.O 

r 

.... 

1.8 

1.8 

0 

o 

300 

t6.7 

3-7 

r 

146.6 

27.6 

Part  V. 


o 

0 

90 

5-o 

2.8 

58.4 

9-7 

o 

o 

60 

5-2 

3-2 

.... 

65.8 

14.7 

o 

o 

180 

5-o 

3-i 

.... 

58.4 

12.9 

*  Representing  about  3,000  nuclei  due  to  nonenergized,  dust-free  air. 
f  Persistence  tested  but  not  found  (2-minute  exposure,  i-minute  lapse, 


=  1.0). 


62        NUCLEATION  OF  THE  UNCONTAMINATED  ATMOSPHERE. 

The  data  of  table  37  were  at  first  obtained  in  the  wooden  fog  chamber. 
It  was  thought  advisable  to  repeat  them  with  the  cylindrical  glass  fog 
chamber,  as  this  could  be  kept  rigorously  free  from  leakage  (curves 
58,  59).  The  mean  results  show  that  about  20  per  cent  of  the  particles 
persist  indefinitely.  This  datum,  which  in  any  case  is  an  inferior 
limit,  is  smaller  here,  because  the  amount  of  subsidence  is  relatively 
greater  in  a  more  shallow  vessel.  Without  condensation,  i.  e.,  in  the 
absence  of  solution,  only  2  to  5  per  cent  of  the  nuclei  persist  after 
i  minute.  With  solution,  the  decay  is  not  appreciably  different  in  i 
to  3  minutes,  showing  that  long  periods  of  persistence  are  in  question. 

60        0.^;,*; *ih~JLJ\.+:-.  Vl^.,  CLio™°»*    i     %F  \   40r 


FIGS.  56-62.— Illustrating  tables  37,  38. 
Tab.  10  in  the  above  chart  is  replaced  by  the  present  table  37 ;  Tab.  u,  by  the  present  table  38. 

50.  Enlargement  of  nuclei  in  dust-free  nonenergized  air.— An  exceed- 
ingly interesting  correlative  result  is  obtained  by  converting  the  nuclei 
of  dust-free  nonenergized  air  into  solutional  nuclei.  Here  the  first 
exhaustion  must  necessarily  be  made  at  a  pressure  difference  (say 


PERSISTENCE  AFTER  SOLUTION. 


8p~  23  cm.  in  the  cylindrical  apparatus)  decidedly  above  the  fog  limit, 
so  that  a  corona  of  appreciable  size  may  appear.  If  this  is  dispelled 
on  admission  of  filtered  air  by  evaporation,  the  second  corona  may  be 
obtained  at  a  pressure  difference  (8p  =  21  cm.  in  the  table)  below  the 
fog  limit,  showing  that  large  nuclei  have  been  produced  by  evapora- 
tion. In  the  data  of  table  38,  or  in  curves  61,  62,  different  intervals  of 
waiting  are  tested,  these  intervals  referring  to  the  time  elapsed  (i  to 
10  minutes)  between  the  evaporation  of  the  first  corona  and  the  con- 
densation of  the  second.  After  3  minutes  about  25  per  cent  of  the 
nuclei  persist  and  require  smaller  exhaustions  to  induce  condensation 
than  the  original  nuclei.  After  10  minutes  about  5  per  cent  are  left 
(curve  60),  though  a  greater  number  of  observations  are  here  desirable. 
It  should  be  noticed  that  without  the  preliminary  condensation  no  con- 
densation whatever  would  take  place  at  the  lower  pressure  difference. 

TABLE  38. — Persistence  in  solution.     Air  nuclei.     Fog  chamber  glass  cylinder. 
8/2  =  23.2  ;  5/1  =  21.4. 


Time  from  first 

Time  from  in- 

exhaustion at 
5^  =  23.2,  to 

flux  to  second 
exhaustion  at 

*fc 

**. 

Ni  X  io-3. 

N*  X  io-3. 

Ratio. 

influx. 

5^  =  21.4. 

Sec. 

Sec. 

0 

60 

4.2 

2.8 

34 

9.4 

.28 

0 

120 

4.9 

3-i 

58 

12.4 

.22 

o 

60 

4.1 

2.6 

3i 

7.8 

.25 

f6o 

30 

4.0 

o 

29 

.0 

0 

60 

30 

4.9 

o 

58 

.0 

0 

o 

180 

4.2 

2.6 

34 

7.8 

•23 

o 

600 

4-5 

i-3 

43 

2.2 

•05 

=  o  always  tested. 


t  Sufficient  for  complete  subsidence. 


51.  Occurrence  of  water  nuclei. — An  explanation  of  the  phenomena 
of  the  preceding  paragraphs  is  not  far  to  seek.  Clearly  the  ions  or 
fleeting  nuclei  go  into  solution,  and  the  result  on  reevaporation  of  the 
fog  particles  is  a  solutional  or  water  nucleus.  Such  a  nucleus  is  ob- 
viously larger  than  the  original  nucleus  or  ion  which  furnishes  the 
solute.  Hence  the  condensation  in  the  succeeding  exhaustion  must 
first  take  place  on  these  residual  nuclei,  and  they  are  therefore  apt  to 
capture  all  the  available  water.  What  makes  the  water  nucleus  stable 
is  either  the  solute,  by  which  the  vapor  pressure  is  reduced  on  con- 
tinued evaporation  to  a  degree  equal  to  the  excess  of  vapor  pressure 
due  to  curvature,  or  possibly  electrical  potential  may  have  a  corre- 
sponding effect. 


64         NUCLEATION   OF  THE  UNCONTAMINATED  ATMOSPHERE. 

It  is  particularly  interesting  that  if  the  nuclei  or  dust-free  nonener- 
gized  air  become  the  solute  of  water  nuclei,  that  the  new  nuclei  require 
pressure  differences  much  below  the  fog  limit  of  the  original  air  for 
condensation,  and  the  solutional  nuclei  are  stable. 

52.  Cause  Of  periodicity.  —  Very  many  of  the  occurrences  which  accom- 
pany condensation  may  be  explained  by  the  result  just  announced. 
In  particular  the  alternations  of  large  and  small  coronas  (cf.  Chapter  II, 
sections  24,  27)  so  frequent  throughout  the  present  work  are  fully 
accounted  for.  The  small  fog  particles,  i.  e.,  those  condensed  on  the 
smaller  nuclei  and  caught  near  the  end  of  the  exhaustion,  evaporate 
into  the  larger  particles  and  become  the  water  nuclei  available  in  the 
next  exhaustion.*  Hence  if  the  other  condensation  nuclei  are  all 
small,  like  those  due  to  weak  radiation  or  those  normally  present  in 
air,  the  next  condensation  will  take  place  on  the  water  nuclei  only. 
Thus  a  small  inferior  corona  follows  the  large  superior  corona  of  the 
primary  exhaustion.  In  the  next  exhaustion  water  nuclei  will  be 
absent,  relatively  speaking,  and  the  condensation  now  occurs  on  all 
the  small  nuclei  available  for  producing  a  large  superior  corona  ;  and 
so  on  in  succession.  In  general  there  are  thus  three  groups  of  nuclei, 
x,  jy,  2,  concerned  in  any  given  condensation  —  a  group,  x>  of  water 
nuclei  from  the  preceding  exhaustion  ;  a  group,  y,  of  nuclei  belonging 
to  the  condensation  in  question  and  corresponding  to  the  observed 
superior  coronas  ;  a  group,  ^,  of  nuclei  belonging  to  the  same  conden- 
sation, but  which  will  evaporate  their  water  and  make  the  water  nuclei 
for  the  next  condensation.  In  case  of  periodicity  the  successive 
exhaustions  would  run, 

1.  y\          z\  Superior  corona  on  y\. 

2.  x%  =  zi  z%=o  Inferior  corona  on  #2. 

3.  #3  —  2-2  —  o;  v%-\-ys  23  Superior  corona  on  _y2  -fjs. 

4.  x±  =  z$  z±  —  o  Inferior  corona  on  x±. 

5.  xz  =  zi  =  o',  y*-}-yb  z§  Superior  corona 


etc.  If  the  nuclei  are  fleeting  the  superior  corona  of  the  n-ih  exhaus- 
tion is  condensed  onjyn  only,  and  under  these  circumstances,  j^n+^n,  the 
total  nucleation  may  often  be  replaced  by  xn-\-yn,  or  the  total  nuclea- 
tion  is  the  sum  of  the  values  belonging  to  the  superior  and  inferior 
coronas.  In  this  way  the  analysis  of  Chapter  II,  sections  28,  29,  admits 
of  easy  interpretation. 

53.  Rain.  —  In  any  exhaustion  the  group  zn  =  xn+l  are  accountable 
for  the  rain  which  almost  always  accompanies  coronal  display.  In 
such  cases  the  water  nuclei  are  comparable  in  smallness  with  the  other 
nuclei,  and  the  former  are  not  able  to  capture  all  the  available  water. 

*  Incidentally  the  medium  is  kept  saturated  while  temperature  rises  after  exhaustion. 


PERSISTENT  NUCLEI. 


In  the  above  charts,  Tab.  12  is  replaced 
by  the  present  table  39;  Tab.  13,  by  the 
present  table  40;  Tab.  14,  by  the  present 
table  41. 


FIGS.  63-68.— Illustrating  tables  39,  40,  41. 

54.  Persistent  nuclei  in  general.— It  is  not  improbable  that  persist- 
ency may  generally  be  due  to  some  cause  favorable  to  the  production 
of  water  nuclei.*  Those  heavy  rains,  for  instance,  which  accompany 
the  X-ray  corona  when  the  bulb  is  close  to  the  fog  chamber  may  be 
due  to  the  fact  that  condensation  occurs  spontaneously  without  the 
need  of  supersaturation ,  if  an  exposure  to  very  intense  X-light  is  in 
question.  The  nuclei  in  the  X-field  behave  like  hygroscopic  bodies. 


*  For  more  detailed  statements  see  my  investigation  on  the   "Structure  of  the 
Nucleus,"  Smithsonian  Contributions,  No.  1373,  1903. 


66 


NUCXEATION   OF  THE  UNCONTAMINATED  ATMOSPHERE. 


TABLE  39. — Fog  limits  of  fleeting  nuclei.     Cylindrical  fog  chamber,  without  casket. 

sz  =  o,  but  tested. 


Exposure  to  — 

Distance. 

«j>. 

51. 

s\. 

TViXio-3. 

A^iXio-3. 

cm. 

50 

21.4 

2.7 

2-7 

8.7 

8.7 

.... 

20.5 

.O 

I.O 

.0 

1.4 

25 

20.5 

2.O 

2.O 

3-o 

3-0 

I.  Radium  in  aluminum  .  .  •< 

19.7 

.O 

.... 

.0 

o 

20.5 

2.8 

2-5 

8.8 

6/4 

.... 

19.7 

.O 

.O 

.0 

.0 

.... 

21.4 

3-9 

4.0 

25.2 

27.2 

• 

200 

21.4 

3-4 

.... 

17.1 

.... 

.... 

20.5 

1.4 

.... 

2.1 

.... 

50 

20.5 

3-4 

2.9 

I6.3 

9.4 

.... 

19.7 

.0 

.O 

.O 

.0 

II.  X-rays  < 

IO 

20.5 

4.2 

3-7 

30.4 

22.1 

19.7 

.0 

.0 

.O 

.O 

5 

20.5 

4-3 

... 

32.8 

.... 

.... 

19.7 

r 

.0 

1.4 

20.5 

3-0 

10.6 

.... 

• 

21.4 

5-3 



66.3 

.... 

TABLE  40. — Fog  limits  of  persistent  nuclei.     Bulb  above. 


Exposure  to  — 

Height 
of  bulb. 

9j, 

**. 

s%- 

M, 

Afc 

Remarks. 

cm. 

r 

•5 

18.0 

(*) 

3-1 

(83) 

10.2 

r 

Radiation  through 

1 

•5 

18.0 

t(8.6) 

3-5 

(118) 

15.3] 

earthed  aluminum 

III.  X-rays,  3m.  .  -j 

2.0 

18.0 

t(6.i) 

3-2 

(78) 

L 

ii.  6 

plate. 
Do. 

5-0 

18.0 

*3.6 

2.2 

17-5 

3-5 

Do. 

IO.O 

18.0 

r 

.0 

1.4 

Do. 

3-o 

18.0 

tM 



4.6 



Do. 

r 

•5 

18.0 

o 

.... 

.0 

.0 

Exposure,  i  min. 

IV.  X-rays           *{ 

e 

IQ.7 

•3    « 

f 

22.2 

I    e 

Do. 

•  J 

•5 

j.y.  / 
197 

3* 

*5-8 

2.O 

17.2 

•"••  J 
2.9 

Exposure,  2  min. 

*  Oblong  corona. 

t  Spindle  or  gourd-shaped  corona. 


J  After  this,  bulb  ( ?)  ceases  to  be  efficient. 


Radium, 


X-rays, 


cm. 
50 

25 
o 

200 
50 

IO 

5 


Foglimit=2o.4 

(20.3) 

20.  i 

20.3 

(20.1) 

(i9.7) 
19-6 


=  9X10" 
(14) 

20 

16 
(24) 

(33) 
(36) 


10 
18 
10 

22 

44 

52 


55.  Gradation  of  size  of  fleeting  nuclei— Fog  limits.— The  preceding 
observations,  as  well  as  the  work  of  Chapter  II,  section  34,  figure  34, 
make  it  probable  that  the  fog  limit  varies  slowly  but  definitely  with 
the  density  of  the  ionization,  while  the  rate,  8  TV/8  (8^),  or  slope  of  the 


SIZE  OF  FLEETING  NUCLEI.  67 

curves,  i.  <?.,  the  increment  of  nucleation  per  centimeter  of  pressure 
difference,  increases  very  rapidly.  It  makes  little  difference  how 
the  ionization  is  produced,  whether  by  instantaneous  exposure  to  the 
X-rays  or  to  other  radiation.  In  fact,  the  curves  become  nearly  ver- 
tical in  relative  steepness.  Additional  experiments  are  nevertheless 
needed,  and  table  39  contains  such  results.  In  the  first  part  radium 
(io,oooX)  in  the  thin  aluminum  tube  is  the  energizer;  in  the  second 
part,  the  X-rays  perform  a  similar  function  more  strongly.  The  results 
may  be  summarized  in  curves  63,  64,  65,  66,  and  as  follows: 

Both  series  are  in  general  agreement  and  indicate  the  extremely  slow 
depression  of  the  fog  limit  (indicating  the  nuclei  of  maximum  size) 
with  the  increase  of  number,  8  NIB  (8p)  (fig.  65).  In  fact,  the  method 
for  measuring  8p  is  rather  too  crude  to  bring  out  the  fog  limits  prop- 
erly. They  may  be  found  from  two  consecutive  measurements  of  N 
for  two  values  of  8p  close  together  and  near  the  fog  limit.  Figures 
65  and  66  contain  a  comparison  between  the  fog  limits,  8pQ,  and 
8  NJ8  (Sp),  as  well  as  N  for  §p  =  2 1  cm. ,  below  the  fog  limit  of  dust-free 
air.  They  show  the  accentuated  variation  of  the  nucleations ;  but 
they  announce  also  the  decided  variation  of  the  fog  limits  for  the  case 
of  fleeting  nuclei,  i.e.,  that  the  maximum  size  of  nucleus  is  a  variable 
quantity  among  the  gradations. 

The  last  part  of  the  table  shows  data  for  the  persistent  nuclei 
(curves  67).  These  were  produced  here  by  placing  the  bulb  above 
one  end  of  the  cylindrical  fog  chamber,  for  the  glass  at  the  bottom 
was  too  thick  to  admit  a  sufficiently  intense  radiation.  The  inevitable 
difficulty  in  the  investigation  of  these  results  is  the  weakening  of  the 
X-ray  bulb  in  continued  use.  In  a  measure,  this  is  a  proof  that  elec- 
trical resonance  or  any  more  direct  induction  is  not  operative,  for 
these  effects  would  not  vary  with  the  past  history  of  the  bulb.  Never- 
theless, to  avoid  the  possibility  of  such  disturbances  an  earthed  sheet  of 
aluminum  was  adjusted  to  cover  the  top  of  the  fog  chamber.  Experi- 
ments showed  that  all  these  precautions  are  unessential. 

The  curves  (67)  show  the  rapid  decrease  of  the  number  of  persistent 
nuclei  with  the  height  of  the  bulb  (measured  from  the  outside)  above 
the  cylindrical  glass  chamber  (walls  0.3  cm.  thick).  They  also  show 
the  extremely  rapid  increase  of  the  nucleation  with  the  time  of  expos- 
ure, suggesting  radio-activity  on  the  part  of  the  nuclei  as  stated  in 
section  56. 

In  table  41  the  endeavor  was  made  to  determine  the  fog  limit  from 
two  observations  of  N  lying  slightly  above  it.  The  work  was  very 
carefully  done,  but  the  data  nevertheless  fail  to  mark  out  definite  loci. 
Beginning  with  the  coronas  for  nonenergized  air  *  (radium  at  infinity), 

*  The  curve  for  air  in  case  of  high  pressure  differences  is  very  difficult  to  deter- 
mine, and  will  again  be  treated  elsewhere. 


68 


NUCLEATION   OF  THE   UNCONTAMINATED   ATMOSPHERE. 


which  are  always  blurred  and  rainy,  the  probability  of  a  curve  doubly 
inflected  near  the  fog  limit  is  apparent,  particularly  if  mean  values  be 
taken  (curves  68). 

Radium  at  D  =  200  and  at  D  =  100  cm.  show  data  lying  very  nearly 
in  this  curve,  but  the  last  observations  of  the  series  prove  that  the  fog 
limit  is  nevertheless  definitely  lower,  or  that  the  largest  groups  of 
nuclei  are  appreciably  larger  than  the  largest  nuclei  in  dust-free  non- 
energized  air. 

TABLE  41. — Fog  limits  of  fleeting  nuclei.     Cylindrical  fog  chamber.     -sa  =  o,  tested. 


Exposure  to  — 

Distance. 

i* 

Si. 

*-, 

MX«r* 

^ 

f 

cm. 

40 

0*7     .4 

oo    o 

3*7 

•3 

37-4 

4O.4 

I    Air  < 

Zj.Z 

•7 

3*o 

25*  3 

22*Q 

OO      0 

20 

2£- 

« 

rt  /^\ 

z**3 

•3 

•5 

4.7 

y.u 

—  _    . 

V. 

•4 

200 

23.2 

3-5 

2*2 

3-7 

2O.6 

4.J 

25-3 

100 

22.3 

2^6 

2-5 

•4 

8.1 

7-5 

°  3    <? 

3         A 

3e 

18  7 

•4 

O 

J.O.  / 

50 

23-2 

3-4 

3-6 

I8.7 

22.9 

O  T    /I 

2  7 

2»7 

8  7 

8   A 

z./ 

o./ 

0.4 

25 

21.4 

2.9 

2.8 

9.9 

9.4 

II.  Radium  in  aluminum  tube  - 

10 

23-2 
23.2 

4.0 
4.0 

3.9 
4.0 

29.7 
29.6 

28.3 
29.6 



21.4 

2.8 

3.1 

9.2 

I3-I 

*0 

21.4 

3.1 

3-4 

17.1 

t(Top) 

23-2 
23-2 

4^8 

4-5 
4.9 

63-7 

54-9 

43-9 
56.7 



21.4 

3-6 

21.  0 

21.  0 

200 

21.4 

1.8 

1.8 

2.7 

2.7 



21.4 

.0 

•5 

.O 

.8 

{ 

50 

19.7 

1.2 

1.7 



20.5 

3.1 

II.7 



III    X-rays  \ 

OT        A 

40 

4.8 

1 

zi.4 

.z 

0*7    o 

0/7    o 



23.2 

5-5 

5-7 

Z/.Z 
80.  I 

Z/.Z 

88.2 

i 

10 

19.7 

2.1 

3c- 

3'4 

2.4 
18.1 

•5 

I 



21.4 

5-3 

4-7 

66.4 

47.0 

*  Radium  15  cm.  from  line  of  sight. 

t  Radium  5  cm.  from  line  of  sight. 

\  Growth  from  5  =  3.3  to  5  =  3.8;  radium  5  cm.  from  line  of  sight. 

Radium  at  D=  10  and  at  D  =  2$  cm.  form  a  similar  group  with  an 
obviously  much  lower  fog  limit,  and  the  case  is  accentuated  for  radium 
at  D=^Q  cm.  from  the  end,  or  15  cm.  and  5  cm.  (on  top)  from  the  line 
of  sight.  At  this  point  the  data  for  the  X-rays  with  the  anticathode  at 


SECONDARY    GENERATION.  69 

distances  D—  10  to  26  cm.  form  a  prolongation  of  the  series,  showing 
further  reduced  fog  limits  and  the  probability  of  a  doubly  inflected 
curve  of  the  same  type  throughout. 

As  a  whole  these  observations  corroborate  what  has  already  been 
inferred,  that  nuclei  of  all  sizes  are  present  simultaneously ;  that  by 
far  the  greater  number  have  a  size  depending  on  the  density  of  the 
ionized  field  by  which  they  are  produced.  These  nuclei  correspond 
to  the  steeper  ascent  of  the  curves.  With  this  given,  the  exception- 
ally large  nuclei  at  the  lower  end  of  the  curve  and  the  exceptionally 
small  nuclei  at  the  upper  end  bring  about  the  double  inflection,  since 
the  numbers  of  each  gradually  vanish.  The  more  intense  the  ioniza- 
tion,  the  more  nearly  are  the  nuclei  of  the  same  size,  while  for  weak 
ionization  the  gradation  shown  by  the  flat  curves  is  accentuated. 

56.  Secondary  generation. — In  table  42  the  endeavor  was  made  to  com- 
pare the  effects  of  the  X-ray  bulb  acting  to  produce  persistent  nuclei 
from  different  distances  from  the  end  of  the  fog  chamber.  Unfortu- 
nately dense  stratified  fogs  occur  in  the  first  exhaustion,  which  makes 
it  necessary  to  use  the  second  exhaustion  for  the  same  nucleation  as 
a  means  of  measurement.  The  pressure  difference  8p  =  2o  cm.  is 
below  the  fog  limit,  when  air  is  not  energized. 

The  first  two  parts  of  the  table  show  the  rapid  decrease  of  TV  with 
increasing  D ;  but  it  is  particularly  remarkable  that  after  the  lapse  of 
2  minutes  subsequently  to  the  exposure,  the  nucleation  (ccet.  par.) 
has  apparently  increased  (curves  74,  76),  precisely  as  if  there  were 
induced  radio-activity  in  the  nuclei,  or  in  the  apparatus,  after  the 
X-radiation  has  been  cut  off.  The  incessant  danger  from  undersatu- 
ration  is  probably  ineffective  in  view  of  the  low-pressure  difference. 
It  follows,  then,  that  the  decaying  nucleus  is  radio-active  (for  which 
reason  probably  the  fleeting  nuclei,  though  instantly  generated,  do 
not  decay  at  the  same  enormous  rates),  or  that  the  larger  nuclei  break 
up  into  smaller  nuclei  (increasing  their  number  about  threefold  on  the 
average),  or  that  small  nuclei  beyond  the  range  of  the  exhaustion 
gradually  grow  to  a  larger  size. 

Special  experiments  to  bring  out  this  feature  of  secondary  genera- 
tion were  made  in  table  42  and  in  the  third,  fourth,  and  fifth  parts  of 
table  43.  The  phenomenon  is  put  in  evidence  strongly  on  all  cases, 
but  with  an  additional  result,  showing  a  tendency  in  the  alternations 
to  disappear  after  several  repetitions  (curves  72,  73).  The  fifth  part  of 
table  43  shows  the  occurrence  of  secondary  generation  even  for  dis- 
tances of  20  cm.  between  the  anticathode  and  the  fog  chamber.  The 
last  datum  is  an  indication  of  the  growth  of  fog  particles  in  the  lapse 
of  time  (curve  75).  In  the  fourth  part  of  table  43  (curve  72)  the  alter- 


70         NUCXEATION    OF  THE   UNCONTAMINATED   ATMOSPHERE. 


nations  are  a  maximum,  while  the  time  elapsed  after  the  exposure 
(4  minutes)  is  longest.  The  amplitude  of  the  alternations  is  in  all 
cases  initially  about  2.5:  i,  but  it  must  be  remembered  that  the 
coronas  are  observed  after  the  second  exhaustions.  The  nuclei  caught 
in  the  first  exhaustions  may  be  estimated  at  50,000  to  100,000. 

TABLE  42. — Secondary  generation. 


Part. 

5/.    D. 

Time  of 
exposure. 
(Rays  on.) 

Time  after 
exposure. 
(Rays  off.) 

Si. 

sz- 

YViXio-3. 

A^Xio"3. 

I 

20     6 

Min. 

2 

Min. 

Q 

Strata 

2.4. 

51 

TC      8 

•4 

J.^.0 

6  2 

*2 

*-j 

6  2 

2 

•*»3 

3T 

o 

2   I 

o 

2  2 

•^ 

o    Q 

2 

3O 

10  *; 

II 

2e       6 

o 

2  8 

•*o    u 

•u 

Spindle  4  8 

oz*4 

I 

o 

4-9 

37 

ZO 
2-3 

64.0 

27  6 



III 

2c     fi 

I 

I 

•/ 

O     Q 

^•4 
2  I 

z/.u 
oo  O 

O 

4-3 

41.0 

*  Fails. 

TABLE  43. — Continuation  of  the  preceding.     Secondary  generation.     D,  distance  of 
X-ray  plate  (anticathode)  of  bulb  from  end  of  fog  chamber. 


Time  of 

Time  after 

D. 

exposure. 

exposure. 

ftp. 

s\. 

sz- 

MXio-3. 

A^Xio-3. 

(Rays  on.) 

(Rays  off.) 

Part  I.  Effect  of  distance. 


cm. 

5 

1  2O 

O 

2O.  I 

Strata. 

3-7 

.... 

21.5 

10 

I2O 

O 

.... 

'  ' 

1.9 

.... 

2.8 

20 

120 

0 

.... 

Fog. 

•5 

.6 

Part  II.  Secondary  generation. 


5 

I2O 

1  2O 

2O.  I 

Dense  strata. 

5-2 

58.0 

10 

1  2O 

1  2O 

Strata. 

2.8 

.... 

8.5 

20 

1  2O 

I2O 

I.O 

.... 

.      d.o) 

PENETRATION    OF  X-RAYS. 


TABLE  43,  continued. — Continuation  of  the  preceding. 


Time  of 

Time  after 

D. 

exposure. 

exposure. 

8fl. 

si. 

s%. 

N\  X  io~3. 

AgXio"3. 

(Rays  on.) 

(Rays  off.) 

Part  III.  Secondary  generation. 


5 

120 

1  2O 

20.  1 

Strata. 

4.2 

.... 

30.0 

5 

.... 

0 

.... 

3-2 

.... 

12.9 

5 

.... 

1  20 

.... 

" 

4-4 

34-3 

5 



o 



4.2 



30.0 

Part  IV. 


5 

120 

O 

20  I 

Strata. 

3-6 

19-5 

.... 

.... 

240 

.  .    . 

5-o 

5i-5 

.... 

.... 

0 

.  .    . 

" 

3-6 

19-5 

.... 

.... 

240 

.  .    . 

" 

4-3 

32.0 



.... 

o 

.  .    . 

4.0 

25.0 

Part  V. 


20 

1  20 

0 

2O.  I 

Veil. 

.... 

Veil  .0 

.... 

.... 

.... 

120 

.... 

2.9 

.... 

9.2 

.... 

— 

240 

O 



3-5 



17.6 

.... 

In  the  first  part  of  table  42  the  alternations  are  promiscuous,  but 
they  fail  but  once  in  8  observations  (curve  71  ;  failure  at*).  In  the 
second  part,  where  the  coronas  are  nearly  measurable,  there  is  no 
failure  (curve  70).  The  third  part  shows  that  exposures  of  i  minute 
are  not  sufficient  to  bring  out  the  phenomenon . 

NUCLEATION  DUE  TO  RAYS  PENETRATING  FROM  A  DISTANCE  OR 
THROUGH  DENSE  MEDIA. 

ST.  Effect  of  distance  of  the  X-ray  bulb  from  the  free  wooden  fog: 
Chamber. — The  probability  of  a  residual  effect  in  case  where  the  X-ray 
bulb  is  moved  to  a  considerable  distance  from  the  fog  chamber  is  sug- 
gested by  many  of  the  above  results.  It  is  worked  out  in  detail  in 
table  44,  where  the  condensations  described  were  all  made  at  the  press- 
ure difference  corresponding  to  the  fog  limit  of  dust-free  non energized 
air,  and  without  cutting  off  the  radiations.  There  is  thus  no  decay. 
Nevertheless,  the  results  are,  as  usual,  disappointingly  irregular,  the 
first  datum  of  each  pair  of  results  being  low,  the  second  high.  Perio- 
dicity therefore  occurs  in  spite  of  the  wet-sponge  tube  added  to  the 
filter.  The  observed  variation  of  results  is  moreover  impossible  in 
relation  to  distance,  even  though  the  data  for  inferior  and  superior 
coronas  are  apparently  consistent  in  both  outgoing  curves.  Again,  in 


NUCLEATION  OF  THE  UNCONTAMINATED  ATMOSPHERE. 


the  return  series  inferior,  superior,  and  mean  coronas  occur  together. 
It  would  be  difficult  to  conjecture  any  reason  for  the  apparent  mini- 
mum at  /?— 50  cm.  and  the  apparent  maximum  at  I}=2oo  cm.,  and 
they  will  presently  be  shown  to  be  referable  to  the  bulb.  In  any  case, 
however,  the  mean  decrement  of  nucleation  within  6  meters  is  certainly 
less  than  one-fourth,  evidencing  an  astonishingly  small  distance  effect. 

TABLE  44. — Nucleating  effect  of  X-radiation  from  different  distances  ;  8$  =  35  cm. 
Time  of  exposure,  i  min.,  prolonged  through  condensation. 


Part 

D. 

Si. 

S2. 

MXio-3. 

N2Xio-s. 

Part. 

D. 

Si. 

S2> 

jViXio-3. 

Nk  Xio~3. 

I. 

5 

*5«i 

2-5 

69.6 

8.0 

II. 

600 

5-4 

r 

83-4 

50 

2.O 

i-3 

3.8 

2.4 

200 

5-4 

r 

83.4 

50 

4.2 

2.0 

38.0 

3-8 

6 

5-5 

r 

87.6 

IOO 

3-4 

2.O 

20.4 

3-8 

t6 

2.7 

.  .  .  . 

IO.O 

IOO 

4.1 

2.O 

35-o 

3-8 

III. 

600 

5-3 

(*) 

79.0 

2OO 

4-3 

1.9 

41.0 

3-6 

200 

5-3 

79.0 

200 

4.9 

2.O 

64.8 

3-8 

6 

5-3 

.  .  .  . 

79.0 

400 

3-3 

1.8 

18.6 

3-2 

IV. 

600 

5-5 

(J) 

87.6 

400 

4.4 

2.1 

60.0 

4.4 

200 

5.6 

92.0 

600 

4.0 

1.6 

32-4 

3-0 

6 

5-6 

.  .  .  . 

92.0 

600 

3-9 

i-5 

31.0 

2.8 

V. 

6 

6.3 

3-1 

123.0 

146 

400 

4-3 

2.O 

41.0 

3.8 

50 

4.9 

(i) 

64.0 

2OO 

4.9 

2.O 

64.8 

3-8 

50 

4.9 

64.0 

IOO 

4-5 

2.O 

48.0 

3-8 

6 

5-2 

74.4 

50 

3-7 

1-3 

27.6 

2.4 

6 

5-2 

.  .  .  . 

74.4 

5 

4.0 

T.7 

32.4 

3-i 

50 

6.0 

112.4 

200 

4-3 

2.O 

41.0 

3-8 

50 

5-4 

•  ... 

83.4 

*  7  cells  in  remaining  experiments. 
f  i  minute  after  exposure. 


\  Taken  but  not  recorded. 


To  guard  against  variations  of  the  tube,  the  abbreviated  series  were 
made  as  given  in  the  second,  third,  and  fourth  parts  of  the  table  (upper 
curves  69);  and  these  show  what  was  to  be  expected  from  the  prelimi- 
nary results,  that  within  the  6  meters  of  observation  about  the  same 
nucleation  is  produced  in  the  fog  chamber  (ccet.  par.)  irrespective  of 
distance.  Finally,  part  V  of  the  table  proves  that  the  apparent  mini- 
mum at  D=  50  cm.  is  an  error. 

The  absence  of  a  distance  effect  in  the  case  of  the  nonincased 
wooden  fog  chamber  is  astonishing  and  implies  that  the  space  within 
the  6  meters  of  observation  is  everywhere  equally  full  of  the  nucleus- 
producing  radiation.  This  behavior,  moreover,  is  different  from  the 
fluorescent,  photographic,  or  even  the  electrical  effect  of  the  X-rays. 
Thus  the  phosphorescent  screen  is  intensely  illuminated  at  /?— 5  cm., 
while  at  2  meters  it  is  very  dim  and  at  6  meters  quite  dark.  It  is  nat- 
ural to  infer  that  the  constancy  of  radiation  is  due  to  atomic  disinte- 
gration of  the  platinum  anticathode,  when  bombarded  by  the  cathode 


GENERATION   AND   DECAY. 


73 


torrent,  and  that  the  issuing  rays  are  akin  to  the  gamma  rays  of  radium 
and  quite  distinct  from  the  undulatory  phenomenon  of  X-radiation. 
In  fact,  each  part  of  the  medium  within  the  radius  of  6  meters  behaves 
as  if  it  were  the  source  of  such  rays. 


Jlldorpti 


5  10          /5 

FIGS.  69-78.—Illustrating  tables  43,  44,  45,  49,  50,  53,  54. 

58.  Generation  and  decay  for  radiation  from  D=200  cm. — Before 
proceeding  with  the  investigation  it  will  be  advisable  to  examine  the 
generation  and  decay  of  nuclei  when  the  radiation  comes  from  long 
distances.  The  data  of  table  45  are  of  the  kind  to  be  anticipated  from 
the  results  of  section  17.  The  experiments  were  made  at  the  fog 
limit  of  dust-free  air.  The  first  part  of  the  table  shows  that  exposures 


74         NUCLEATION   OF  THE   UNCONTAMINATED  ATMOSPHERE. 


of  i  and  2  minutes  produce  about  the  same  nucleation,  which  vanishes 
with  the  lapse  of  i  or  2  minutes  after  exposure  to  negligible  residues. 
In  the  second  part  of  the  table  the  radiation  is  stronger  and  maximum 
nucleation  appears  after  3  seconds  of  exposure,  so  that  the  nucleation 
is  produced  instantaneously.  Initial  nucleations  obtained  (cat.  par.) 
in  air  which  has  been  long  stagnant  are  apt  to  be  very  low.  The 
mean  nucleation  after  less  than  3  seconds'  exposure  is  about  90,000 
per  cubic  centimeter. 

The  effect  of  longer  exposures  is  again  investigated  in  the  third  part 
of  the  table,  but  the  possibility  of  a  slight  increase  of  the  nucleation 
in  the  lapse  of  time  is  negatived  by  the  last  observation.  The  fourth 
part  also  shows  that  fog  limit  to  be  at  Bp  —  2o  cm.,  and  that  there  is 
no  accumulation  of  nuclei  as  time  goes  on.  There  is  no  appreciable 
persistence. 

TABLE  45. — Generation  and  decay  of  nuclei.      D  =  200.     S^>  =  25  cm.     Wood  fog 

chamber. 


Part. 

if. 

D. 

Time  of 
exposure. 
(Rays  on.) 

Time  after 
exposure. 
(Rays  off.) 

Si. 

52. 

AiXio-3. 

A^Xio-3. 

Min. 

Min. 

I. 

25 

200 

i 

o 

4.2 

i-7 

38.0 

3-0 

i 

i 

2.6 

r 

9.2 

r 

25 

200 

2 

o 

3-7 

i-7 

27.6 

3-0 

2 

2 

1.8 

I.O 

3-2 

2.0 

Sec. 

II. 

25 

200 

60 

0 

*3-6 

i-7 

25.0 

3-0 

5 

O 

6.1 

2.4 

115.0 

6.6 

3 

O 

5-3 

.... 

79.0 

.... 

3 

O 

t4-3 

.... 

41.0 

.... 

3 

O 

5-9 

2.2 

108.0 

5-o 

3 

o 

5-7 

2.O 

96.4 

3-8 

3 

o 

*3.6 

.... 

25.0 



3 

0 

5-6 

2.8 

92.0 

10.4 

3 

0 

5-7 

2.7 

96.4 

10.4 

III. 

25 

200 

10 

0 

4.9  ' 

.... 

63.0 

.... 

10 

o 

4.2 



38.0 



3° 

o 

5-2 

.... 

74-4 

.... 

30 

o 

5-2 

74-4 

.... 

60 

o 

5-3 

.... 

79.0 

.... 

60 

o 

5-4 

2.6 

83-4 

9.2 

3 

o 

5-i 



69.6 



IV. 

20 

200 

3 

o 

r 

r 

r 

r 

30 

o 

i-7 

.... 

2.6 

.... 

60 

o 

«-7 

.... 

2.6 

.... 

1  20 

0 

J-7 

r 

2.6 

r 

*  After  long  waiting.     Stagnant  air.  f  Follows  preceding  high  nucleation. 

As  a  whole  the  observations  for  D  =  200  are  irregular,  for  the  usual 
reasons  instanced  above. 


PENETRATION   OF   X-RAYS. 


75 


59.  Electrical  effect  for  different  distances. — To  roughly  estimate  the 
state  of  the  room  in  relation  to  the  ionizing  effects  of  the  X-rays,  the 
time  of  collapse  of  the  gold  leaves  was  taken,  when  the  galvanoscope 
standing  on  an  earthed  brass  plate  was  covered  with  a  glass  bell  jar. 
Table  46  needs  no  explanation.  In  the  second  part  of  the  table  the 
time  of  collapse  decreases  about  as  the  square  of  the  distance  and  is 
thus  quite  different  from  the  fog-chamber  effect.  At  short  distances 
the  galvanoscope  registers  a  sudden  throw  when  the  circuit  through 
the  X-ray  tube  is  first  made.  The  effect  of  this  throw  is  the  same  as 
if  negative  electricity  entered  the  metal  frame  of  the  electroscope,  and 
it  is  therefore  probably  electrostatic  induction  on  the  brass  foot  plate 
coming  from  the  cathodal  conductor. 

TABLE  46. — Electrical  effects  of  X-rays.     Galvanoscope  in  glass  bell  jar,  walls  0.5  cm. 

thick. 


D. 

Remarks. 

Time  of 
collapse. 

cm. 
200 

15 
50 

TOO 
2OO 
600 

Sec. 
<5 

With  semicylindrical  lead  screen  and  semicircular  li 

30-40 

>  120 
30 

Observed. 
Instantaneous. 

3-    4 
8     10 

-f-  charge  :   impulsively  increased  divergence  ;  then 

collapse, 

—  charge  :  impulsively  decreased  divergence  ;  then 

collapse, 
0.2  sec. 

2 

8 

30 
270 

+  charge*  ) 

—  charge     f 
-f  charge  ) 

—  charge  1 
+  charge  \ 

25-30 
Say  300 

—  charge  f 
+  charge  ) 

—  charge  J 

*  Positive  and  negative  charges  behave  alike. 

60.  Apparent  penetration  of  the  X-rays  coming  from  600  cm — The 

astonishingly  small  distance  effect  observed  made  it  seem  probable 
that  the  effective  rays  are  of  a  penetrating  kind.  Table  47  (to  be  inter- 
preted later)  apparently  bears  this  out,  though  in  reality  it  merely 
separates  the  axial  and  lateral  radiations.  Advantage  is  taken  of  the 
sufficiency  of  short  exposures  whereby  the  tube  is  kept  more  constant. 
The  apparatus  is  shown  in  figure  41,  where  A  is  the  fog  chamber  and 
P  the  plates. 

To  take  first  the  experiments  in  table  47,  when  the  distance  between 
the  lead  screen  at  the  fog  chamber  and  the  X-ray  bulb  is  D  =  600  cm. , 
which  are  smoothest  (curve  79),  it  appears  that  a  single  lead  plate  0.14 


76         NUCLEATION   OF   THE  UNCONTAMINATED  ATMOSPHERE. 


cm.  in  thickness  is  more  than  sufficient  to  reduce  the  nucleation  one- 
half.  Thereafter  the  remaining  thicknesses  up  to  i  cm.  or  more  does 
not  reduce  it  further.  A  close  comparison  is  given  at  the  end  of  the 
work,  in  which  N=  76,000  falls  off  to  N=  32,000  for  6  plates,  or  a 
thickness  of  about  0.84  cm.  (curve  81). 

An  interesting  comparison  is  given  for  the  efficiency  of  the  X-ray 
tube  radiating  from  this  distance  either  from  the  front  face  of  the  anti- 
cathode  or  from  the  rear  face  of  the  anticathode,  the  tube  in  the  latter 
case  being  completely  reversed  (curve  80).  The  mean  results  are 
respectively  ^=42,500  and  ^=34,600,  showing  the  anticathode  to 
behave  as  if  it  were  transparent  or  at  least  radiating  from  both 
faces  in  all  directions.  Indeed,  even  if  the  anode  and  the  cathode  are 
exchanged  (reversed  current),  considerable  radiation  is  sent  out;  as, 

for  instance, 

Concave  mirror  the  cathode,  ^=47,000, 
Concave  mirror  the  anode,      N=  7,000, 

or  about  16  per  cent  of  the  nucleation  has  been  retained  (curve  80). 
The  coronas  obtained  when  lead  screens  are  used  in  front  of  the  fog 
chamber  are  clear  and  often  multi -annular,  showing  the  nuclei  to  be 
very  nearly  of  a  size. 

1.   (  .l-U: 


<e         -v         i-o        /#        /•«•        i-e 

FIGS.  79-82. — Illustrating  table  47. 

In  the  above  chart  Tab.  20  =  present  table  47. 


7-8 


PENETRATION   OF  X-RAYS. 


77 


TABLE  47. — Penetration  of  rays  and  reversal  of  tube;  5^  =  25  cm.  Exposure  about 
3  sec.  prior  to  condensation  without  cutting  off  the  radiation;  air,  5=  1.2;  wood 
fog  chamber  not  cased  (fig.  41). 


Part. 

D. 

si. 

52. 

A^iXio-3. 

A^Xio"3. 

Remarks  on  penetration. 

I. 

200 

5-4 

3.2 

83.4 

16.6 

Screens  removed. 

5-4 

83.4 

Tin  plate,  0.50  mm.  thick. 

4-3 

'(*)' 

41.0 

.... 

Lead  plate,  1.4  mm.  thick. 

4-5 

.... 

48.0 

.... 

Lead  plate,  2.8  mm.  thick. 

4-5 

.... 

48.0 

.... 

Lead  plate,  2.8  mm.  thick. 

5-4 

— 

83.4 



Screen  removed. 

II1. 

6OO 

5-2 

.... 

74-4 

.... 

Do. 

3-9 

r 

31-0 

.... 

Lead  plate,  2.8  mm.  thick. 

6OO 

4.2 

r 

38.0 

.... 

Screen  removed.     Tube  reversed. 

4-3 

r 

41.0 

Screen  removed.     Tube  directed. 

3-9 

r 

31.2 

.... 

Screen  removed.     Tube  reversed. 

4.4 

r 

44.0 

.... 

Screen  removed.     Tube  directed. 

600 

2.6 

.... 

9.2 

.... 

Anodal  rays. 

2.2 



5-0 



Do. 

II. 

600 

4.2 

r 

f38.o 

.... 

o  lead  plate,  1.4  mm.  thick. 

5-o 

.... 

67.0 

.... 

Do. 

t3-7 

.... 

27.6 

.... 

i       do.,  thickness,  1.4  mm. 

3-7 

.... 

27.6 

.... 

Do. 

§3-7 

.... 

28.0 

.... 

2      do.,  total  thickness,  2.8  mm. 

3-7 

.... 

27.6 

.... 

Do. 

4.0 

.... 

32.4 

.... 

4      do.,  total  thickness,  5.6  mm. 

3-8 

.... 

30.0 

Do. 

3-8 

.... 

30.0 

.... 

6      do.,  total  thickness,  8.4  mm. 

3-7 

.... 

27.6 

.... 

Do. 

3-7 

.... 

28.0 

.... 

Do. 

4.0 

.... 

32.4 

.... 

8       do.,  total  thickness,  1  1.  2  mm. 

3-8 

.... 

30.0 

.... 

Do. 

5-4 

I.O 

83-4 

1.8 

o      do. 

4.0 

.... 

32.0 

.... 

6      do. 

5-i 

i*5 

69.6 

2.8 

o      do. 

III. 

6 

5-4 

V 

87.6 

.... 

o  plate. 

6 

5-3 

79.0 

.... 

i  plate. 

6 

5-3 

'(2)' 

79.0 

.... 

o  plate. 

6 

5-3 

(2) 

79.0 



i  plate. 

IV. 

600 

5-3 

(2) 

79.0 

.... 

i  plate. 

600 

**4.o 

(2) 

79.0 



o  plate. 

V. 

200 

5-3 

(2) 

79.0 

.... 

o  plate. 

200 

5-3 

(2) 

32-4 

.... 

i  plate. 

200 

4-5 

(2) 

48.0 

.... 

2  plates. 

4-3 

(2) 

41.0 

.... 

4  plates. 

4.4 

(2) 

44.0 

.... 

8  plates. 

5-1 

(2) 

69.6 

.... 

o  plate. 

5-2 

(2) 

74-4 



o  plate;  i  min.  exposure;  no  growth. 

*  Second  exhaustion  made,  but  not  recorded. 

f  Initial  low  datum. 

\  Galvanoscope  discharged  at  6  meters  and  through  lead  plate,  but  much  more  slowly 
than  the  instant  collapse  at  6  cm. 

§  First  plate  filters  out  the  axial  rays.  The  remainder  have  no  observable  effect,  and 
are  virtually  transparent.  Coronas  clear  and  multi-annular  apart  from  rain. 

]f  Second  exhaustion  necessary  to  avoid  periodicity. 

**Note  the  reduction  of  A^at  600  for  i  plate,  which  does  not  occur  at  D  =  6  cm. 
and  D  =  200  cm. 


78         NUCLEATION  OF  THE  UNCONTAMINATED  ATMOSPHERE. 


TABLE  47,  continued. — Penetration  of  rays  and  reversal  of  tube,  etc. 


Part. 

D. 

Si. 

s*. 

AiX  io~3. 

^V2X 

I0~3. 

Remarks  on  penetration. 

VI. 

7 

6.4 

2 

129.0 

o  plate. 

5-4 

2 

83-4 

i  plate. 

5-3 

2 

81.2 

2  plates. 

5-9 

. 

108.4 

o  plate. 

5-7 

. 

96.4 

4  plates. 

4.9 

. 

64.8 

7  plates. 

5-6 

. 

92.0 

4  plates. 

4.9 

• 

64.8 

o  plate. 

VII. 

200 

4-7 

•X-) 

56.0 

o  plate,  thickness,  o.o  cm. 

4.9 

. 

64.0 

o  plate,  thickness,  o.o  cm. 

4.4 

. 

44.0 

i  plate,  thickness,  0.14  cm. 

4.1 

. 

35-o 

i  plate,  thickness,  0.14  cm. 

5-6 

. 

92.0 

o  plate,  thickness,  o.o  cm. 

. 

69.6 

o  plate,  thickness,  o.o  cm. 

4-5 

. 

48.0 

i  plate,  thickness,  0.14  cm. 

4-7 

. 

56.0 

i  plate,  thickness,  0.14  cm. 

5-3 

81.2 

o  plate,  thickness,  o.o  cm. 

4.2 

. 

38.0 

7  plates,  thickness,  0.98  cm. 

4-3 

. 

41.0 

7  plates,  thickness,  0.98  cm. 

4.2 

. 

38.0 

12  plates,  thickness,  1.68  cm. 

5-6 

. 

92.0 

o  plate,  thickness,  o.o  cm. 

600 

5-5 

• 

• 

87.6 

o  plate,  thickness,  o.o  cm. 

*  Taken,  but  not  recorded.     In  the  first  two  data  the  bulb  is  gaining  strength. 

61.  Apparent  penetration  of  the  X-rays  coming  from  200  cm.  and  from 
6  to  <T  cm. — The  results  for  D=  200  cm.  are  similar  to  the  preceding. 
It  again  takes  less  than  one  lead  plate  (thickness  0.14  cm.)  to  stop  the 
absorbable  rays  (curve  82).  There  is  no  extra  thickness  of  lead  as 
an  equivalent  of  the  layer  of  400  cm.  of  air  removed.  Again,  about 
one-half  of  the  radiation  is  stopped  by  the  first  plate  and  greater  thick- 
nesses produce  no  further  effect.  At  the  end  of  the  table  a  wall  of 
lead  1.7  cm.  thick  shows  no  additional  absorption.  Moreover,  tinned 
iron  plate  ^  mm.  thick  has  no  appreciable  effect  on  the  radiation 
whatever  (curve  82). 

The  first  experiments  for  D  —  6  cm.  show  apparent  previousness  of 
the  single  lead  plate  (0.14  cm.  thick);  but  this  seems  to  be  referable 
to  the  intensity  of  the  initial  radiation  without  the  lead  screen ,  for  in 
the  experiments  at  D=  7  cm.,  a  single  plate  shows  marked  reduction 
of  the  very  large  coronas  observed.  On  the  other  hand,  a  plate  even 
i  cm.  thick  absorbs  very  little  of  the  radiation,  for,  roughly,  about  80 
per  cent  passes,  in  spite  of  the  indefinite  thickness  of  lead,  between  the 
bulb  and  the  fog  chamber,  completely  screening  off  the  latter.  The 
results  throughout  are  curiously  irregular  and  difficult  to  interpret,  as 
seems  not  unexpected,  since  all  secondary  radiators  must  now  be  close 
at  hand  (curve  83). 


PENETRATION   OF  X-RAYS. 


79 


TABLE  48. — Penetration  ;  miscellaneous  experiments  on  case  of  lead  plates  ;  0.14  cm. 
thick  ;  5j^  =  25  cm.     Wood  fog  chamber. 


Part. 

D. 

Rays  on. 

Rays  off. 

Number 
of  plates. 

si. 

* 

«x~i 

*X»rt 

Sec. 

Sec. 

I. 

7 

3 

60 

o 

2.7 

.... 

10.4 

.... 

60 

60 

o 

3.2 

.... 

16.6 

.... 

120 

60 

0 

Strata  (5.7) 

3-2 

96.0 

16.6 

120 

o 

o 

Fog      (5.0) 

(2) 

68.0 

.... 

120 

60 

i 

Veil       2.7 

1.4 

10.4 

2.6 

120 

60 

i 

Veil       3.0 

1.4 

13.2 

2.6 

II. 

7 

180 

60 

i 

Veil       3.0 

.... 

12.2 

.... 

1  2O 

60 

o 

Strata  (4.8) 

3-4 

6o.O 

20.4 

Case  of  tinned  iron  plate,  0.5  mm  thick. 

III. 

6 

3 

o 

o 

5.6 

92.O 

180 

0 

o 

Strata  (6.8) 

3.1 

153-0 

180 

I2O 

o 

Strata  (7.1) 

3.1 

I7O.O 

180 

o 

I 

5-8 

2-3 

IOI.O 

180 

I2O 

I 

2.O 

r 

3-8 

3 

o 

0 

5.8 

(3) 

IOI.O 

3 

60 

0 

2.7 

r 

10.4 

IV. 

*6 

1  20 

60 

I 

2.9 

r 

ii.  8 

r 

1  20 

o 

o 

4.0 

2.8 

32-4 

10.4 

*  Another  bulb. 

62.  Generation  through  lead  plate  and  through  iron.— The  data  of 
table  48  show  the  usual  accelerated  increase  of  the  nucleation,  N,  with 
the  time  of  exposure,  when  nuclei  of  the  persistent  type  are  produced 
(curve  84).  When,  however,  the  lead  screen  (thickness  0.14  cm.) 
intervenes,  there  is  no  accelerated  increase  and  no  accumulation  above 
a  relatively  small  value,  N=  13,000.  These  nuclei  may  be  a  transi- 
tional type,  but  it  is  difficult  to  interpret  the  case  of  very  small  coronas. 
Another  similar  test  was  made  with  a  screen  of  tinned  sheet  iron  ^ 
mm.  thick.  The  results  are  in  the  main  the  same ;  in  other  words, 
marked  persistent  nucleation  is  not  produced  through  the  iron  plate 
in  spite  of  its  slight  thickness  and  lower  density.  Parallel  observa- 
tions for  3  seconds '  exposure  show  that  about  as  many  nuclei  are  thus 
generated  as  are  obtained  after  a  3-minute  exposure  through  the  plate. 

On  the  other  hand,  for  3  minutes'  exposure  there  is  growth  of  nuclea- 
tion, if  observation  is  made  2  minutes  after  exposure ;  in  the  presence 
of  the  plate  the  nucleation  falls  off  to  a  negligible  datum  in  the  same 
lapse  of  2  minutes  after  exposure.  The  decrement  in  this  case  is  of 
the  same  order  as  is  observed  for  the  short  exposure  (3  seconds)  tested 
a  minute  after  exposure  ceases.  The  use  of  another  bulb  with  the 
plate  does  not  change  the  results. 


80         NUCLEATION   OF  THE  UNCONTAMINATED  ATMOSPHERE. 


FOG  CHAMBERS   INCLOSED  IN  METAL  CASKETS. 

63.  Wood  fog  chamber  in  lead  casket— Penetration.— In  table  49  data 
of  a  crucial  kind  are  given  for  the  purpose  of  separating  the  radiation 
which  actually  passes  the  lead  screens  from  that  derived  from  second- 
ary or  lateral  sources.  The  first  part  of  the  table  is  at  once  decisive 
(curves  77).  Less  than  7  per  cent  of  the  radiation  which  passes  the 
wood  and  glass  walls  of  the  chamber  will  pass  through  the  front  face 
(toward  the  bulb),  if  this  face  is  closed  by  a  lead  plate  0.14  cm.  thick. 
When  the  chamber  is  freed  from  the  casket  and  the  plate  placed  at  the 
bulb,  more  than  half  of  the  radiation  gets  into  the  fog  chamber  sec- 
ondarily, as  shown  in  the  second  part  of  the  table  and  curve  77. 

TABLE  49. — Wood  fog  chamber  in  a  lead  casket,  open  in  front,  toward  the  bulb. 
D  ='200  cm  ;  8p  =  25  cm.  Thickness  of  lead  plate,  0.14  cm  ;  of  glass  plate,  0.7  cm. 
Exposure,  3  sec. ;  lapse,  o  sec. 


Part. 

Front  of  casket,  etc. 

s\. 

S2. 

MXio-3. 

A^Xio-3. 

I. 

Open,  bulb  4  

51 

1.7 

69  6 

30 

Open 

66  o 

•2    8 

Closed  by  lead  plate  

.u 

"3 

^  8 

So 

do  

5.O 

50 

Open  .  . 

4.6 

si.  6 

jl 

Open   bulb  o  

5.O 

I  7 

66  o 

Closed  by  lead  plate   

2  8 

A*/ 

no 

.u 

Casket  removed    

A    8 

2  o 

60  o 

•4 
?  « 

Lead  plate  cit  bulb  

40 

I  7 

•32    A 

j'° 

do  ,  

3Q 

I  7 

or  2 

.u 

do  

37 

I  7 

27  6 

•3    O 

Glass  plate  

47 

I.Q 

56  o 

o  6 

III 

Open 

6  ^ 

fi  fi 

do 

*»«o 

•*«4 
I  7 

.z 

2.7 

*w 

2.7 

74*4 
IO.O 

.u 
10  o 

Closed  by  2  lead  plates 

2  O 

6  6 

,  8 

Closed  by  4  lead  plates 

^•4 

2  6 

j>0 

Closed  by  o  lead  plate 

•&O 

2  O 

'4 

5r»* 

2  8 

Closed  by  glass  plate 

•j 

I  7 

^•° 

Closed  by  tin  plate 

4Q 

6^  O 

.u 

Lead  plate  at  bulb 

3n 

2  A. 

T  o   2 

6  6 

With  an  improved  and  more  fully  lead-incased  chamber,  the  data 
given  in  the  third  part  of  the  table  were  investigated,  in  which  succes- 
sive thicknesses  of  0.14,  0.28,  0.42  cm.  of  lead  plate  allow  14,  9,  and 
7  per  cent  of  the  radiation  to  pass  (curve  78).  The  differences  from 
the  above  datum  are  due  to  the  greater  intensity  of  the  radiation  here 
applied  and  to  other  incidental  conditions.  Furthermore,  a  glass  plate 
0.7  cm.  thick,  and  a  tinned  iron  plate  0.05  cm.  thick,  each  allow  nearly 
all  the  radiation  to  pass,  /.  e.,  about  90  per  cent,  while  a  lead  plate 
placed  near  the  bulb  at  D  =  200  cm.  cuts  off  about  17  per  cent  of  the 
radiation  (curve" 78). 


PENETRATION   OF  X-RAYS. 


8l 


Hence  it  follows  in  the  above  experiments  with  the  lead  envelope 
removed,  since  one-half  of  the  radiation  was  cut  off  by  a  single  frontal 
lead  plate  0.14  cm.  thick,  that  about  half  of  the  radiation  enters  the 
wooden  fog  chamber,  not  from  primary,  but  from  secondary  sources 
(using  this  term  in  its  broadest  sense),  through  the  lateral  walls  of  the 
apparatus.  When  the  chamber  is  inclosed  in  the  lead  case  open  in 
front,  the  inside  walls  of  the  lead  become  a  source  of  radiation,  so  that 
the  corona  need  not  decrease  in  size,  as  the  data  show.  In  general, 
the  behavior  is  such  as  if  the  whole  medium  between  the  bulb  and 
chamber  were  equally  *  'polarized"  (to  use  this  word  with  a  special 
meaning).  At  the  lower  pressure  difference  (8/>  =  2o  cm.)  the  lead 
plate  proves  to  be  quite  impervious,  but  the  tin  plate  certainly  admits 
an  accumulation  of  3,000  nuclei. 

64.  Continued — Radiation  from  a  distance. — Experiments  made  to 
find  the  effect  if  the  distance,  D,  of  the  bulb  from  the  lead-incased 
fog  chamber,  open  toward  the  bulb  only,  are  given  in  table  50. 

TABLE  50. — Wood  fog  chamber  in  lead  casket.     Effect  of  distance,  D.     5$  =  25  cm. 
Exposure,  3  sec  ;  lapse,  o  sec. 


D. 

Si. 

jYiXio-3. 

Mean. 

cm. 

600 

*4-o 

32.4 

38 

3-7 

27.6 

.... 

200 

4.9 

62.0 

50 

6 

4-3 

41.0 

50 

6 

4.8 

60.0 

.... 

200 

4.2 

38.0 

.... 

600 

4.4 

44.0 

.... 

*s%  always  taken,  but  not  recorded.     Usually  s2=  1.5  cm. 

The  bulb  is  as  usual  variable,  but  the  nucleation  produced  is  about 
the  same  for  all  distances  up  to  200  cm.,  after  which  there  is  a  possible 
decrease  of  about  one-fifth  as  far  as  600  cm.,  the  limit  of  observation 
(curves  69).  This  relatively  insignificant  effect  of  distance  is  again 
remarkable,  inasmuch  as  all  remote  secondary  radiation  is  excluded. 
Whatever  produces  the  nucleation,  if  secondary,  must  come  from  the 
inside  of  the  casket,  or  it  must  be  primary.  At  all  events  it  is  again 
manifest  that  the  whole  medium  within  the  room  is  almost  equally 
energized  throughout. 

Table  51  and  curve  85  show  the  penetration  of  tinned  iron  plates, 
each  0.5  mm.  in  thickness,  when  the  X-ray  bulb  is  600  cm.  from  the 
lead-cased  fog  chamber.  Several  millimeters  of  iron  plate  are  still 


8  2        NUCLEATION   OF  THE  UNCONTAMINATED  ATMOSPHERE. 


appreciably  penetrable  even  from  this  remote  distance.  So  far  as  the 
data  go  the  absorption  is  relatively  marked  between  0.5  and  i  mm.  of 
thickness,  the  rates  being  much  larger  here  than  for  greater  or  smaller 
thicknesses. 

TABLE  51. — Penetration  of  tinned  iron  plates,  0.05  cm.  thick.     Z>— 600  cm. 
$2  =  25  cm.     Wood  fog  chamber  in  lead  casket. 


Number 
of  plates. 

Total 
thickness. 

Si. 

TViXio-3. 

Mean. 

cm. 

o 

0.00 

*4.o 

32-4 

32 

i 

05 

3-6 

25-0 

25 

2 

10 

2.2 

5-o 

8 

2 

IO 

2.8 

II.  2 

.... 

4 

20 

2.2 

5-o 

5 

4 

20 

2.1 

4.4 

.... 

0 

OO 

3-9 

32.0 

36 

i 

05 

3-7 

27.6 

28 

2 

IO 

2.8 

II.  2 

ii 

4 

20 

2.4 

6.6 

7 

o 

OO 

4-3 

41.0 

.... 

flC 


*  Second  exhaustion  made,  but  not  recorded.     Usually  s%—i.o. 


e&««^&4  •#«•.&£ 

JOE*.**]    d-^M.  $7>.<S   ''' 

^  •    »      . ' -i*— 


'^Sec^       «0  40  60     ...  80      .       /W  /«;  740  ^60 


FIGS.  83-87. — Illustrating  tables  47,  51,  53,  54. 


PENETRATION   OF  X-RAYS. 


TABLE  52. — Distance  effect  of  X-rays.     Glass  fog  chamber.     8^  —  22  cm.  (fog  limit 
of  air).     No  lead  casket.     Walls,  0.3  cm.     Bottom  i  cm.  thick. 


Distance. 

si. 

sa. 

MXio-3. 

A^Xio-3. 

cm. 

200 

4.6 

*i.6 

51-6 

3-o 

4-3 

i-7 

41.0 

3-2 

10 

5-o 

i-5 

67.0 

2.6 

5-o 

i-5 

67.0 

.... 

600 

3-4 

1-5 

20.4 

.... 

3-5 

1-5 

22.6 

.... 

200 

3-7 

r 

27.6 

.... 

4.4 

r 

44.0 

.... 

10 

5-3 

r 

7Q.O 

.... 

5-0 

r 

67.0 



*  Faint  and  small,  due  to  dust-free  air. 

TABLE  53. — Distance  effect  of  X-rays.     8^  =  22  cm.     Lead  plate  0.14  cm.  thick, 
sg  =  o,  but  always  tested. 


Distance. 

Lead  plates. 

Si. 

AiXart 

Distance. 

Lead  plates. 

«. 

WX«* 

Part  I.  Cylindrical  fog  chamber,  without  casket. 


200 

I 

3-2 

13-9 

200 

0 

4.3 

34-4 

o 

4.8 

50.4 

IO 

0 

5-o 

55-4 

*0 

3-7 

23.2 

600 

O 

3-3 

15-6 

I 

3.8 

25.2 

o 

3-i 

12.2 

Part  II.  Cylindrical  fog  chamber,  lead-cased,  with  tubular  end  of  lead  50  cm.  long. 

(Fig.  42.) 


50 

o 

4-7 

47.0 

4OO 

O 

3-5 

19.0 

I 

1.8 

2.7 

0 

3-6 

21.0 

I 

2.O 

3-2 

200 

o 

3-8 

25.2 

2 

1.8 

2.7 

0 

4.1 

29.4 

O 

4.8 

50.0 

50 

0 

5-o 

55-4 

2OO 

O 

3.6 

21.  0 

o 

5-0 

56.3 

O 

3.7 

23-2 

50 

I 

i-5 

2.3 

600 

O 

3-o 

II.  I 

I 

J-5 

2-3 

0 

3-i 

12.3 

Part   III.   Lead-cased   fog    chamber    as    before.     Penetration   through  tinned  iron 

plates  0.05  cm.  thick. 


Distance. 

Tin 
plates. 

s\. 

MXio-8. 

Per  cent 
transmitted. 

50 

i 

3.8 

25.2 

46 

2 

3.7 

23.2 

42 

5 

2.5 

6.7 

12 

3 

3.2 

13-9 

25 

i 

I** 
1+7 

47.0 
47.0 

j-         86 

0 

5-o 

55-0 

100 

:  Double  glass  envelope. 


84         NUCIvEATlON   OF  THE  UNCONTAMINATED  ATMOSPHERE. 

65.  Glass  fog:  chamber— Radiation  from  a  distance.— The  experiments 
on  the  nucleation  produced  by  X-rays  coming  from  a  distance  were 
now  continued  by  aid  of  the  cylindrical  fog  chamber  (glass  walls  0.3 
mm.  thick  and  i  cm.  thick  at  the  bottom),  the  lead  casket  being  here 
removed  (curve  69).     The  data  are  given  in  table  52,  and  may  be 
restated  from  the  mean  results, 

D=    o-|~3o  cm.  ^=70,000, 

200  4-  30  41,000, 

620  -f-  30  22,000, 

where  TV  is  measured  from  the  line  of  sight,  30  cm.  from  the  end  of 
the  fog  chamber  nearest  the  bulb.  Very  much  of  the  lateral  radia- 
tion is  thus  cut  off  by  the  thick  glass  walls  and  bottom  of  the  fog 
chamber;  but  the  decrements  are  far  from  suggesting  the  law  of 
inverse  squares  even  in  a  remote  degree.  As  the  distance  from  the 
line  of  sight  increases  over  20  times,  ^decreases  only  3  times. 

The  repetition  of  these  experiments  with  a  less  active  bulb  gave 
about  the  same  results  (table  53).  For  distances  from  the  line  of  sight, 
D=20,  210,  610,  the  average  nucleation  was  ^=55,000,  34,000, 
14,000.  About  one-half  the  total  radiation  is  absorbed  by  a  frontal 
lead  plate,  or  a  double  glass  envelope,  as  usual  (curves  69). 

66.  Radiation  from  a  distance— Glass  fog  chamber  in  lead  case.— The 
endeavor  was  finally  made  to  stop  off  all  secondary  radiation  by  pro- 
viding a  close-fitting  lead  tube  (£,  fig.  42),  which  not  only  incased 
the   fog  chamber   A,  but   extended   about  50  cm.  beyond   the   end 
nearest  the  bulb.     If  distances  are  measured  from  the  line  of  sight, 
the  mean  results  may  be  estimated  as  Z?  =  6o,  210,  610  cm.,  corre- 
sponding to  NX  io~3  =  52,  25,  12.     The  nucleation  falls  off  a  little 
more  rapidly  than  before  (a  part  of  which  may  be  referable  to  imper- 
fect alignment  of  the  distant  bulb),  but  after  200  cm.  the  decrease  is 
slow  (curves  69). 

In  the  present  case  a  single  lead  plate  (thickness,  0.14  cm.)  cuts  off 
nearly  all  the  radiation,  i.  e.,  all  but  4  to  6  per  cent.  Hence  very 
little  secondary  radiation  has  entered,  while  the  small  penetration  of 
the  lead  is  probably  referable  to  the  distance  of  the  plate  from  the  end 
of  the  chamber  (cf.  distance  effect  for  gamma  rays,  next  paragraph). 
Compared  with  lead,  the  absorption  of  tinned  iron  is  small  (curves  86), 
the  plates  (eventually  0.25  cm.  thick)  allowing  26  per  cent  of  the  radi- 
ation to  pass  for  the  same  thickness  of  plate  which  was  used  in  the 
case  of  lead.  This  result  is  quite  out  of  proportion  with  the  relative 
densities. 


EFFECT  OF  RADIUM.  85 

NUCLEATION  DUE  TO  GAMMA  RAYS. 

6<T.  Lead-cased  wooden  fog  chamber — Penetration, — In  order  to  in- 
terpret the  above  data  for  X-rays,  it  will  first  be  necessary  to  deter- 
mine the  facility  with  which  nuclei  are  produced  by  very  penetrating 
radiation.  The  radiation  of  radium  filtered  through  lead  walls  about 
i  cm.  thick  was  therefore  tested.  Table  54  gives  a  series  of  results  in 
which  the  radium  (io,oooX)  was  first  tested  when  hermetically  sealed 
in  a  thin  aluminum  tube  and  placed  6  to  10  cm.  from  the  line  of  sight 
(curve  87).  In  this  case  the  radiator  nearly  touched  the  free  end  of 
the  lead-cased  fog  chamber  A  (fig.  43).  The  aluminum  tube  was  then 
successively  enveloped  in  one  or  more  lead  tubes,  T,  with  wall  0.5 
cm.  in  thickness.  The  length  of  the  tubes  exceeded  the  width  of  the 
fog  chamber,  and  they  were  placed  with  their  axes  parallel  to  the 
plane  of  the  end,  so  that  any  radiation  entering  would  have  to  pass 
through  the  lead  ;  or,  passing  out  of  the  lead  tube,  enter  the  fog  cham- 
ber laterally  under  very  unfavorable  conditions.  L,eaving  the  latter 
case  (which  is  here  negligible)  for  further  experiment,  table  54  gives 
the  coronal  apertures  $i,  s2,  ss,  etc.,  and  nucleations  A^,  JV2,  JVS,  etc,, 
found  in  successive  exhaustions  under  the  conditions  stated.  The 
figures  show  that  periodicity  is  a  frequent  and  unavoidable  occurrence. 
Many  exhaustions  were  therefore  made  in  each  case  and  the  means 
taken  in  triads.  These  are  given  in  detail  in  the  summary  at  the  end 
of  the  table,  and  in  the  curve  (87).  Sometimes  the  particular  adjust- 
ment of  the  tube  (as,  for  instance,  the  position  of  the  radium  in  the 
tube)  seems  to  be  of  importance,  for  the  results  in  any  given  position 
are  fairly  uniform.  An  additional  lead  plate  is  ineffective.  The 
summary  shows  that  of  the  radiation  which  escapes  from  the  alumi- 
num tube,  85  per  cent  passes  through  0.5  cm.  of  lead  and  70  per  cent 
through  i  cm.  of  lead,  assuming  that  there  is  no  secondary  radiation. 
In  one  case  (tube  capped  by  a  lead  plate)  nothing  at  all  seems  to  enter 
the  fog  chamber.  This  suggested  the  following  group  of  experiments, 
which  show  that  zero  nucleation  may  occur  periodically  under  any 
conditions. 

68.  Continuation. — The  new  results  (table  54,  part  IV)  show  a  curious 
irregularity,  which  is  borne  out  by  the  behavior  of  radium  when 
placed  in  the  fog  chamber  (Chapter  II,  section  31).  In  the  present 
case  the  tube  was  60  cm.  long  (similar  to  P}  fig.  44),  parallel  to  the 
plane  of  the  end  (about  20  cm.  across)  of  the  fog  chamber  and  placed 
close  to  it.  The  data  for  the  open  and  closed  tube  are  about  the 
same.  In  both  cases  the  values  of  N  at  times  descend  to  the  low 
nucleations  of  nonenergized  air,  though  as  a  whole  they  lie  pro- 


86        NUCLEATION  OF  THE  UNCONTAMINATED  ATMOSPHERE. 


nouncedly  above  it.  The  lead  tube  without  radium  is  inactive. 
Moreover,  in  the  final  part  of  the  work  all  data  are  decidedly  lower 
than  at  first,  as  if  the  energizing  quality  were  fatigued.  This  occurs 
not  only  within  the  radium  in  lead  tubes,  sealed  or  not,  but  in  the 
case  where  the  radium  is  in  the  sealed  aluminum  tube  only.  The  air 
values  give  evidence  of  an  almost  entire  absence  of  nuclei.  Reasons 
for  this  unsatisfactory  behavior  can  not  even  be  conjectured.  The  mean 
values  given  in  thousands  per  cubic  centimeter  are :  For  air,  TV*  —2.6; 
radium  in  open  lead  tube,  TV  =2  2— 12  ;  radium  in  capped  lead  tube, 
N—2I  — 18  ;  air,  N=2.2\  lead  tube  without  radium,  N=2.\  ;  radium 
in  aluminum  tube  only,  N=  10 ;  radium  in  open  lead  tube,  N=  7 ; 
radium  in  capped  lead  tube,  N =7  ;  air,  TV— o,  remembering  that  the 
radium  is  in  all  cases  surrounded  by  the  sealed  thin  aluminum  tube. 

Apart  from  the  fatigue  it  is  clear  that  the  open  and  capped  tube 
behave  alike,  proving  that  the  rays  actually  penetrate  the  walls  and 
that  secondary  radiation  is  ineffective.  This  also  follows  from  the 
next  paragraph,  as  the  distance  effect  of  radium  is  marked.  The 
amount  of  radiation  passing  5  mm.  of  lead  is  here  about  73  per  cent, 
but  the  present  result  is  not  as  good  as  the  above. 

TABLE  54. — Penetration  of  7-rays  of  radium.  8p  =  25  cm.  Lead-cased  fog  chamber. 
Radium  in  thin  (o.i  mm.)  aluminum  tube,  hermetically  sealed.  Walls  of  each  lead 
tube  0.5  cm.  thick.  Plate,  0.14  cm.  thick.  Z>  =  6-iocm.  Lead  tubes  parallel 
to  walls  of  chamber,  20  cm.  long. 


Part. 

Remarks. 

Si. 

s, 

S3- 

*, 

A^iXio-3 

A^Xio-3 

^XXO- 

I. 

Radium  in  Al  only  

Radium  in  lead  tube... 
Radium  with  i  plate 
and  tube  

2.9 
3-3 

2  7 

3-2 

1.9 

2  6 

3-0 

2  7 

2.8 
1.9 
2  "^ 

n.8 
18.6 

IO.4 

16.6 
3-6 

9.2 

13.2 
13.2 

IO.4. 

II.  2 

(n.8) 
3-6 

8  o 

Radium  in  lead  tube... 
Radium  with  reflector.. 
Radium  in  lead  tube... 

2.9 
I.O 

2.6 

2.9 

2.1 
2.6 

3-2 
2.O 

I  O 

2.7 

2-3 
2  O 

n.8 
1.8 
9.2 

2  8 

n.8 
4.4 
9.2 

2.8 

16.6 

3-8 

2.8 

i  8 

(10.4) 
10.4 

5-4 
o  8 

XI 

Radium  removed  

**3 

I  A. 

2.2 

I.O 

2.6 

1.8 

Radium  in  Al  tube  
Radium  in  lead  tube... 

Radium  in  double  lead 
tube  

2.7 

1.8 
2  8 

2.8 
2.7 

I  Q 

2.O 
2  Q 

3-2 
1-5 

I.O 

IO.O 

3.2 

10  6 

10.6 

IO.O 

3.6 

3-8 
13-2 

ii  8 

16.6 

2.8 

(18.6) 
i  8 

Radium  in  double  lead 
tube  

I.O 

2  2 

•3,  -3 

1.8 

13.2 

(5-4) 
18  6 

i  6 

I  O 

I  7 

I  O 

30 

i  8 

i  8 

A'/ 

' 

*  Given  in  thousands  per  cubic  centimeter. 


PENETRATION   OF  GAMMA   RAYS. 


TABLE  54,  continued.  —  Summary. 


Part- 

Radium  at  oo. 

Radium  in 
Al  tube. 

Radium  in 
i  lead  plate  ; 
wall  0.5  cm. 

Radium  in 
2  lead  tubes  ; 
wall  i  cm. 

Miscellaneous. 

Tube  and 
plate. 

Tube  and 
reflector. 

III. 

(  2.5 

JI4-5 
(  11.9 

J    9-8 
\    8.4 

|  7-4 

1     5-2 

9.8 
9.2 

3-6 

[3.9 

(2-7 

j    8.8 
1    8.7 

J  13-0 

J    8-3 

(    10.5 

JM 

(2.4 

(    7.6 
J    5-0 

I   9-3 

Means..   2.7 

ii.3 

9-5 

7'9 

9-5 

3-6 

TABLE  54,  continued. — Tubes  of  lead  60  cm.  long  often  capped.    Wall,  0.5  cm.  thick. 


Part. 

Remarks. 

Si. 

* 

S3- 

Si. 

MXXO-3 

AiXior* 

^sXio-3 

^XIO- 

IV 

Air  

o 

2.O 

2.O 

o.o 

3.O 

3.8 

3.8 

Radium  in  Al  in  lead 
tube  with  ends  open.. 

"Dn 

3.8 

T    ft 

3-2 

3-3 

2.6 

29.0 

16.6 

22  6 

18.6 

9.2 

Radium  in  lead  tube 

3*5 

37 

30 

.4 
20  4 

16.6 

27.6 

18.6 

•4 

.z 
o 

2  O 

32 

20  4 

o 

3.8 

16.6 

Air  

•4 

1.6 

1.8 

3.0 

1.8 

Lead     tube     without 

*r 

I  O 

T 

1.8 

3.6 

1.8 

Radium  in  Al  tube  
Radium  in  lead  tube 
open  
Radium  in  lead  tube 
capped  
Air 

2.9 

2.2 

2.7 

2.0 
2-3 

3-o 
r 

2.2 



n.8 
5-0 

10.4 
o 

3-8 
14.6 

5-4 
o 

13.2 
1.8 
5-0 



*  No  induced  radio-activity. 

69.  Continued — Effect  of  distance. — Radiations  from  radium  are  in 
curious  contrast  with  the  corresponding  results  for  the  X-rays,  inas- 
much as  the  corresponding  nucleating  power  falls  off  rapidly  with  the 
distance  of  the  sealed  aluminum  tube  from  the  fog  chamber.  At  200 
cm.  the  effect  is  but  just  appreciable  above  the  nucleation  of  nonener- 
gized  dust-free  air,  as  shown  in  table  55. 

Marked  excess  of  nucleation  is  observed  within  ioocm.,  apparently 
increasing  as  the  distance  from  the  fog  chamber  decreases  ;  but  it  is 
difficult  to  make  definite  statements  here,  because  all  the  effects  are 
small  and  successive  exhaustions  show  marked  periodicity.  The 
mean  values  are  estimates.  Though  5  minutes  of  exposure  was  at 
first  allowed,  the  effect  is  probably  instantaneous  and  the  succeeding 
sections  show  that  the  effect  is  very  penetrating. 


88        NUCLEATION   OF  THE  UNCONTAMINATED  ATMOSPHERE. 


TABLE  55. — Radium  effect  from  different  distances  outside  of  fog  chamber.  §^=25 
cm.  Wood  fog  chamber  in  lead  casket.  First  exposure  5  min.  Radium  in  sealed 
aluminum  tube. 


D. 

Si. 

S2- 

S3. 

MXio-3. 

A^Xio-3. 

A^X  io-3. 

Mean 
yVXio-3. 

cm. 

600 

o.o 

.... 

.... 

0.0 

.... 

.... 

0 

400 

1.9 

r 

.... 

3-6 

r 

2 

200 

2.O 

r 

.... 

3-8 

r 

.... 

2 

IOO 

2.6 

2.2 

r 

9.2 

5-o 

r 

7 

50 

3-1 

1-7 

.... 

14.6 

3-0 

.... 

9 

25 

3-2 

I.Q 

*3-i 

16.6 

3-5 

14.6 

10 

10 

3-o 

r 

*3-i 

13.2 

r 

14.6 

8 

0 

3-4 

2.0 

*3-3 

20.4 

3-8 

18.3 

12 

oo 

1.2 

1.8 

fV 

2.2 

3-2 

r 

2 

*  Five  or  six  periods  observed  in  succession,  same  amplitude. 
\  Radium  effect  lost  at  once  ;  apparent  air  periods. 

ft).  Glass  fog  chamber— Penetration — It  seemed  necessary  to  repeat 
the  work  on  the  penetration  of  radium  radiations  as  well  as  the  exper- 
iments on  their  effect  from  a  distance  with  the  aid  of  the  cylindrical 
fog  chamber  of  glass  ;  for  a  vessel  of  this  type  may  be  made  rigorously 
tight,  whereas  entire  freedom  from  leakage  is  often  difficult  to  main- 
tain in  the  plate-glass  apparatus.  From  what  has  been  stated,  leaks 
of  any  kind,  even  if  small,  are  favorable  to  the  occurrence  of  water 
nuclei  and  therefore  to  periodicity.  The  data  are  given  in  table  56 
and  curves  88. 


Slculwm,  Jlwcrrpticn  w  J%  fyhA-. 


D-0     20      40       60       80       100      120     140      160      180     £00 

FIGS.  88-90.-— Illustrating  table  56. 


PENETRATION  OF  GAMMA  RAYS. 


89 


TABLE  56. — Penetration  of  radium  radiation.     Cylindrical  glass  fog  chamber  without 
casket.     5^  =  22  cm.     Lead  tube,  30  cm.  or  60  cm.  long.     Walls,  0.5  cm.  thick. 


Part. 

Remarks. 

Dis- 
tance. 

s\. 

sz> 

S3- 

A^iXio-8 

A^Xio-3 

A^sXio-3 

T 

Radium  in  i  Pb  tube,  capped.. 
Radium  in  i  Pb  tube,  cap  off.. 
Radium  in  i  Pb  tube,  cap  on.. 
Radium  in  i  Pb  tube  cap  off.. 

o 
o 
o 

4.4 

3-4 
2.7 

3-7 

.u 

3-7 
2.7 

3-i 

•A 

3-7 
3-7 
3-9 

44.  u 
20.4 
10.4 
27.6 

18  6 

J-^.Z 

27.6 
9.8 
14.6 

J5'u 

27.6 
27.6 
30.0 

Radium  at  oo*  

CO 

•y 

Radium  in  2  Pb  tubes,  cap  off.. 
Radium  in  2  Pb  tubes,  cap  on.. 

0 

o 

3-4 
3-3 

3.3 

3-3 

3-2 
3-2 

20.4 
18.6 

18.6 
18.6 

16  6 

16.6 
16.6 

IO 

o 

10 

30 

IOO 
20O 

5° 
fo 

o 
2.9 
3-6 
3-i 
2-3 
1.9 

i«5 

2.1 

4-7 

•* 

2.8 

2.4 

3-1 
2.4 
1.9 
i-5 

2.2 
2.7 

•7 
2.9 
3-6 
3-2 
3-o 
1.9 
i-5 

2.2 
3-9 

n.8 
25.0 
14.6 

5-4 
3.6 

2.8 

4.4 
56.0 
o 

II.  O 

6.6 
14.6 
6.6 
3-6 

2.8 

5-o 
27.6 

z/.u 
11.8 
25.0 
16.6 
13.2 
3-6 

2.8 

5«o 
30.0 
o 

*  Air  effect  frequently  tested. 


f  Flat  against  chamber. 


In  the  first  part  of  table  56  the  radiation  passes  through  thick  lead 
tubes,  P,  placed  parallel  to  and  contiguous  with  the  end  of  fog  cham- 
ber Ay  as  shown  in  fig.  88.  There  is  no  observable  effect  due  to  the  cap, 
nor  to  the  length  of  the  lead  tubes,  whence  it  follows  that  the  rays  pro- 
ducing the  nuclei  actually  pass  through  the  heavy  walls  of  lead.  If 
mean  values  be  taken  for  the  periodic  data,  the  results  are  (curve  89) : 

Radium  in  thin  sealed  aluminum  tube,    N  =  27,000 

Radium  in  lead  tube,  walls  0.5  cm.,         JV=  23,000 

walls  1,0  cm.,         N  =  18,000 

or  85  per  cent  and  67  per  cent  pass,  respectively,  through  the  walls  of 
lead  0.5  cm.  and  i  cm.  thick.  The  important  result  follows  here,  as 
above,  that  the  extremely  penetrating  rays  are  responsible  for  the 
observed  nucleation. 

Tl.  Radiation  from  a  distance. — It  is  surprising  to  compare  with  the 
penetrating  effect  of  the  radiation  the  relatively  marked  diminution  of 
its  intensity  with  distance.  Indeed,  if  distances  be  reckoned  from 
the  line  of  sight  (supposing  this  to  be  justified)  about  10  cm.  from  the 
end  of  the  chamber,  the  mean  data  are  (curve  90) : 

D—  10  20  40  60  no  210  cm. 
^Xio-3^  30  13   8   5    3    2 
ND  X  io~*  =  30  26  32  30   33   42 


90        NUCLEATION   OF  THE   UNCOXTAMDSTATED  ATMOSPHERE. 

where  the  decrease  is  about  inversely  as  the  distance,  except  at  long 
distances,  when  the  data  become  uncertain.  All  this  is  in  strong 
contrast  with  the  X-ray  effect,  where  the  removal  of  the  bulb  to  a 
distance  is  so  much  less  significant  than  the  presence  of  a  dense  screen 
in  the  path  of  the  rays. 

T2.  Distribution  of  nucleation  along  the  axis  within  the  fog:  chamber.— 
This  makes  a  final  anomalous  feature  of  the  results.  Whereas  the 
nucleating  effect  falls  off  nearly  25  per  cent  when  the  radium  is  placed 
axially  at  a  distance  of  40  cm.  from  the  end  of  the  fog  chamber,  out- 
side of  it  the  size  of  the  coronas  is  about  the  same  from  end  to  end  of 
the  inner  length  of  about  40  cm.,  no  matter  what  may  be  the  position 
of  the  radium  outside.*  It  will  be  remembered  that  the  decay  and  gen- 
eration of  the  nucleus  is  so  nearly  instantaneous,  that  convection  or 
like  discrepancy  is  quite  out  of  the  question.  These  observations  are 
difficult  because  of  the  short  length  of  the  chamber  and  the  rapid  sub- 
sidence ;  but  so  far  as  they  have  gone,  there  seems  to  be  an  entire 
contrast  between  the  behavior  of  the  radiation  outside  of  the  chamber 
and  the  behavior  inside  of  it,  the  aluminum  tube  being  in  every  case 
outside  of  the  chamber  and  axial  in  position. 

SUMMARY  AND  CONCLUSIONS. 

73.  General  remarks — The  results  of  this  chapter  relate  to  fleeting 
nuclei  (ions),  to  persistent  nuclei,  to  fog  limits,  to  persistence  of  fleet- 
ing nuclei  or  ions  on  solution,  to  the  alternations  of  large  and  small 
numbers  of  efficient  nuclei  in  successive  identical  exhaustions,  to  the 
secondary  generation  of  nuclei  after  intense  X-radiation,  to  the  dis- 
tribution of  radiation  in  the  space  surrounding  the  X-ray  tube  in  con- 
trast with  the  corresponding  case  of  the  sealed  tube  with  weak  radium, 
to  the  nucleation  produced  by  the  gamma  rays  and  its  distribution 
within  the  fog  chamber,  etc.  They  are  thus  of  considerable  impor- 
tance in  their  bearing  on  the  present  research,  and  will  therefore  be 
advantageously  summarized  at  the  end  of  this  memoir,  in  Chapter  VI, 
section  91  et  seg.,  in  connection  with  other  relevant  matter. 

*  The  statement  in  the  text  needs  correction.  My  recent  experiments  have  shown 
that  there  is  an  axial  gradation  of  the  number  of  fleeting  nnclei  within  the  fog  cham- 
ber. This  gradation  becomes  very  marked  when  the  fog  chamber  consists  of  parts 
which  are  unequally  strong  secondary  radiators.  Discussion  will  be  made  elsewhere. 


PLATE  I. 


CHAPTER  IV. 

THE   NUCLEATION   OF  THE  ATMOSPHERE   AT  BLOCK   ISLAND. 

BY  ROBINSON  PIERCE,  JR. 

T4.  Introductory. — The  present  series  of  experiments,  during  the 
winter  of  1904-5,  was  undertaken  with  a  view  to  comparing  the  nucle- 
ation  in  pure  country  air  with  the  results  obtained  at  the  same  time 
in  Providence.*  After  a  consideration  of  several  places,  Block  Island, 
R.  I.,  was  chosen  as  a  station,  on  account  of  its  location,  in  the  ocean 
(see  fig.  94)  10  miles  south  of  Point  Judith,  and  the  freedom  from 
smoke  and  other  refuse  commonly  found  in  the  air  of  cities.  At  the 
same  time,  the  two  stations  are,  in  other  respects,  meteorologically 
nearly  identical.  Through  the  courtesy  of  Prof.  Willis  L.  Moore, 
chief  of  the  United  States  Weather  Bureau,  the  office  of  the  Bureau 
on  the  island  was  placed  at  our  disposal,  and  the  apparatus  was  duly 
installed  there  during  the  latter  part  of  November.  The  chief  occu- 
pations on  Block  Island  are  fishing  and  farming,  and  the  only  smoke 
is  that  from  dwellings,  which  are  to  a  great  extent  scattered.  As  the 
high  readings  usually  occurred  with  north  to  west  winds,  the  situa- 
tion of  the  Weather  Bureau  building  northwest  of  the  village  gave 
complete  freedom  from  all  such  local  influences. 

I  have  here  to  express  my  thanks  to  Mr.  W.  I«.  Day,  the  local 
observer,  for  his  assistance  in  many  ways  during  my  stay  at  the  island. 
Mr.  Day  took  the  observations  at  various  times,  and  the  results  from 
March  10-14  and  April  19-25  are  his. 

ft>.  Apparatus. — The  apparatus  used  was  similar  to  that  employed 
by  Professor  Barus,  f  and  the  two  were  operated  side  by  side  for  some 
time  previous  to  leaving  Providence,  with  results  well  in  accord.  A 
brass  cylindrical  trough  was  substituted  for  the  wooden  one  late  in 
December  and  a  few  minor  changes  were  made  from  time  to  time,  all 
of  which  were  tested  to  make  sure  that  they  did  not  affect  the  read- 
ings of  the  instrument. 

*C.  Barus  :  Smithsonian  Contributions,  Vol.  xxxiv,  1905,  Chap.  IX;  also  Chap.  V 
of  the  present  memoir, 
t  Barus  :  Loc.  cit. 


92         NUCLEATION   OF  THE  UNCONTAMINATED  ATMOSPHERE. 


In  the  following  table  the  weather  is  given  in  terms  of  F  fair,  Fc 
partly  cloudy,  C  cloudy,  R  rain,  Sn  snow,  S  sun ;  the  wind  directions, 
in  points  of  the  compass.  The  coronal  angular  diameter,  <£,  is  such 
that  30  X  2  sin  <£/2  =  s,  or  nearly  <j>  —  5/30,  when  the  eye  at  the  goniom- 
eter and  the  source  of  light  were  at  distances  85  cm.  and  250  cm., 
respectively,  from  the  fog  chamber  between  them.  TV  is  not  corrected 
for  the  temperature  (°C.)  of  the  apparatus,  this  being  added  in  the  next 
table.  The  reduction  from  5  to  N  is  made  as  in  Barus's  memoir 
(Smithsonian  Contributions,  1905,  Vol.  xxxiv),  and  the  measurement 
of  s  made  to  the  outer  edge  of  the  red  ring,  coinciding  with  the  inner 
edge  of  the  blue  or  green  rings.  Exhaustions  were  made  to  a  pressure 
difference  of  8p  =  17  cm. 

TABLE  57. — Successive  observations  of  the  nucleation  (A7"  in  thousands  per  cubic  cen- 
timeter) of  the  atmosphere  at  Block  Island. 


Date. 

V 

H 

Weather. 

1 
F 

Temperature 
of  appara- 
tus. 

Temperature 
of  atmos- 
phere. 

Aperture  s. 

i 

a  6 

2° 

O 

o 

Number, 
n  X  10-3. 

Remarks. 

1904. 

°C 

°F 

Nov.  26 

3  5 

F' 

NW 

18.0 

38 

._ 



I,eaky  trough. 

3.8 

F' 

NW 

18.0 

38 





Do. 

4.4 

F 

NW 

15.0 

38 

3.1 

10.2 

New  trough. 

4.6 

F 

NW 

14.5 

37 

2.8 

7^3 

27 

9.8 

C 

No  wind 

17.8 

34 

2.2 

cor 

3  3 

9.9 

C 

No  wind 

18.0 

34 

2.7 

cor 

6.6 

12.7 

CSn 

SW 

17.6 

31 

3.0 

cor 

9.3 

12.8 

CSn 

SW 

17.7 

31 

3.0 

cor 

9.3 

2.5 

C' 

NW 

18.0 

32 

2.2 

cor 

3.3 

4.2 

C' 

NW 

17.6 

32 

4.3 

w  b  p 

28.0 

Possibly  some  warm  air 

5.0 

C' 

NW 

18.3 

32 

2.3 

cor 

4.0 

28 

9.5 

F 

NW 

15.0 

25 

2.6 

cor 

5.9 

10.4 

F 

NW 

14.8 

24 

2.6 

cor 

5.9 

11.8 

F 

NW 

15.0 

23 

3.1 

cor 

10.2 

2.5 

F 

NW 

14.8 

26 

3.3 

w  b  cor 

12.5 

3.7 

F 

NW 

15.0 

26 

3.2 

cor 

11.3 

5.0 

F 

NW 

15.0 

25 

3.1 

cor 

10.2 

29 

9.5 

C 

SW 

15.2 

37 

2.2 

cor 

3.3 

12.0 

C 

S 

16.2 

3.4 

w  b  cor 

13.8 

1.5 

C 

s 

16.4 

— 

3.6 

w  b  cor 

16.2 

3.1 

C 

s 

16.7 

— 

2.6 

cor 

5.9 

4.2 

C 

s 

17.0 

_  _ 

2.3 

cor 

4.0 

5.5 

C 

s 

17.0 

50 

2.3 

cor 

4.0 

Repeated  same. 

30 

9.3 

C 

SW 

16.6 

47 

1.4 

cor 

1.4 

Rain  at  night. 

10.9 

C 

SW 

16.9 

49 

1.3 

cor 

1.3 

Thick,  almost  foggy. 

12.0 

C 

SW 

17.8 

50 

2.0 

cor 

2.5 

1.5 

C 

SW 

17.6 

49 

1.8 

cor 

1.9 

3.1 

__ 

— 

17.3 

48 

1.7 

cor 

1.8 

4.1 

C' 

sw; 

17.0 

48 

2.0 

cor 

2.5 

5.3 

C' 

SW 

16.8 

47 

1.8 

cor 

1.9 

Dec.     1 

8.4 

C' 

w 

18.8 

34 

2.2 

cor 

1.3 

10.8 

C' 

w 

18.5 

36 

1.7 

cor 

1.8 

11.2 

C' 

w 

18.5 

36 

1.9 

cor 

2.2 

12.1 

C' 

w 

18.5 

36 

2.1 

cor 

2.7 

2.0 

C' 

w 

18.2 

37 

2.2 

cor 

3.3 

3.5 

C' 

w 

18.2 

37 

2.2 

cor 

3.3 

2 

5.6 

8.7 

C' 
C 

w 

NW 

18.3 
16.3 

36 
33 

2.0 
1.4 

cor 
cor 

2.5 
1.4 

Very  faint  ;  influx  tube 
shortened  from  34  to 

14  feet. 

9.1 

C 

NW 

16.3 

33 

1.4 

cor 

1.4 

10.8 

C 

NW 

16.6 

32 

1.9 

cor 

2.2 

12.2 

C 

NW 

16.8 

32 

1.9 

cor 

2.2 

NUCLEATION   AT   BLOCK   ISLAND. 


93 


TABLE  57. — Successive  observations  of  the  nucleation,  etc. — Continued. 


Date. 

V 

H 

Weather. 

•d 

a 

S 

Temperature 
of  appara- 
tus. 

Temperature 
of  atmos-  • 
phere. 

Aperture  *. 

Corona  col- 
ors. 

Number. 
n  X  10-3. 

Remarks. 

1904. 
Dec.    2 

3 

4 
5 

1.8 

3.8 
5.3 
8.6 
10.3 
12.4 
2.9 
4.4 
5.4 
9.1 
12.4 
2.7 
6.7 
8.4 
10  5 

C 
C' 
C' 
C 
C 
CSn 
CSn 
C 
C 
C' 
C 
C 
C 
F 
C 

NW 
NW 

NW 
NE 
NE 
NF, 
NE 
NF, 
NE 
NW 
NW 
W 

w 

NE 
E 

°C 
17.0 
16.9 
16.9 
15.5 
15.6 
16.1 
16.1 
15.3 
15.5 
15.6 
15.6 
16.1 
16.2 
15.0 
15  6 

op 

32 
32 
31 
27 
28 
28 
29 
29 
30 
25 
27 
30 
30 
27 
31 

2.8 
2.2 
2.4 
1.8 
2.0 
1.6 
2.2 
2.9 
2.7 
1.7 
2.9 
3.1 
2.3 
1.5 
1  6 

cor 
cor 
cor 
cor 
cor 
cor 
cor 
cor 
cor 
cor 
cor 
cor 
cor 
cor 

7.3 
3.3 
4.6 
1.9 
2.5 
1.6 
3.3 
8.3 
6.6 
1.8 
8.3 
10.2 
4.0 
1.5 
1  6 

12  3 

C 

SE 

16  3 

33 

1  6 

1  6 

2  1 

c 

SE 

16  5 

34 

1  i 

1  i 

3  7 

Sn 

s 

16  8 

33 

2  1 

2.7 

5  2 

Sn 

s 

16  4 

33 

2  0 

2  5 

Snow  fell,  3.5  inches. 

6 

8.9 

F 

NW 

14.5 

30 

1.6 

1.6 

10  7 

F 

NW 

14  9 

32 

2  9 

8  3 

12  3 

F 

NW 

15.3 

33 

2.6 

5.9 

1.9 
3  4 

F 
F 

NW 
NW 

15.8 
16  1 

32 
32 

3.0 
2  9 

w  bp 

9.3 
8  3 

5  6 

F 

NW 

16  5 

31 

2  7 

6.6 

7 

9.2 
10  5 

C 

c 

sw 
sw 

16.5 
16  0 

36 

36 

1.5 
2  3 

cor 

1.5 
4.0 

12.5 

2.7 

C' 

c 

sw 

sw 

16.1 
16  1 

36 
37 

2.5 

2.7 



5.2 
6.6 

4.0 
5  2 

c 
c 

w 
w 

16.5 

16  8 

37 
38 

3.0 
2  6 



9.3 
5  g 

g 

9  0 

C  Sn 

sw 

16  6 

31 

2  5 

5.2 

' 

10  5 

Sn 

sw 

17  0 

33 

2  5 

5  2 

12  3 

Sn 

w 

17  4 

35 

2  6 

5.9 

1  9 

Sn 

w 

17  5 

35 

2  9 

8.3 

3  5 

Sn 

w 

17  6 

37 

2.0 

2.5 

5  3 

Sn 

w 

17  5 

35 

2  1 

2.7 

9 

8  6 

F 

NW 

14  1 

23 

2  1 

2  7 

9  9 

F 

NW 

14  0 

24 

2  4 

4.6 

11  3 

F 

NW 

13  9 

24 

2  5 

5  2 

12  7 

F 

NW 

14  0 

26 

3  0 

9.3 

2  6 

F 

NW 

13  3 

25 

3  7 

17.5 

4  3 

F 

NW 

14  0 

24 

3  7 

17.5 

5  4 

F 

NW 

14  4 

24 

3  0 

9.3 

10 

8  7 

c 

NE 

13  4 

18 

Too  small  to  measure. 

12  2 

c 

N 

13  4 

17 

1  9 

2.2 

1  8 

c 

N 

12  2 

18 

2  8 

7.3 

Hand  pump. 

5  3 

Sn 

N 

11  0 

18 

20 

2.5 

11 

10  0 

F 

NW 

10  0 

15 

Oil  lamp. 

11  6 

F 

NW 

10  6 

16 

4  7 

37  2 

Hand  pump. 

12  8 

F 

NW 

11  0 

17 

39 

20.5 

Do. 

3  1 

p 

NW 

10  8 

20 

3  6 

16  2 

Do. 

6  8 

F 

NW 

11  0 

22 

2  8 

7.3 

Do. 

12 

9  1 

c 

SE 

13  6 

31 

Too  small  to  measure. 

10  5 

c 

SE 

14  6 

32 



Do. 

12  0 

c 

SE 

14  9 

33 

1  3 

1.3 

3  4 

C  Sn 

NE 

14  6 

31 

Do. 

13 

4.8 
9  2 

Sn 
Sn 

NE 

N 

14.8 
11  6 

31 
24 

1.9 
3  0 



2.2 
9.3 

9  4 

Sn 

N 

11  8 

24 

2  7 

6.6 

10  7 

Sn 

N 

11  9 

24 

2  6 

5.9 

12  1 

Sn 

N 

12  0 

24 

2  9 

8.3 

2  7 

c 

N 

12  0 

26 

2  9 

8.3 

14 

4.8 
9.0 
10.8 
12.3 
2.5 
4.6 
5.3 

C 
F 
F 
F 
F 
F 
F 

NW 
NW 
NW 
NW 
NW 
NW 
NW 

11.9 
12.0 
12.0 
12.3 
12.1 
12.7 
12.5 

28 
15 
16 
17 
17 
17 
19 

3.5 
3.7 
4.7 
4.7 
4.9 
3.8 
3.7 

w  p  cor 
w  p  cor 
w|b|p 
w  P  cor 
w|b|p 
w  P  cor 
wPcor 

15.0 
17.5 
37.2 
37.2 
41.7 
19.0 
17.5 

94        NUCLEATION  OF  THE  UNCONTAMINATED  ATMOSPHERE. 


TABLE  57. — Successive  observations  of  the  nucleation,  etc. — Continued. 


Date. 

1 

Weather, 

| 

5 

Temperature 
of  appara- 
tus. 

Temperature 
of  atmos- 
phere. 

Aperture  s. 

Corona  col- 
ors. 

Number. 
n  X  10-3. 

Remarks. 

1904. 
Dec.  14 

15 

9.3 
11.3 

8.9 
11  0 

F 

F 

c 
c 

NW 
NW 

MB 

NE 

°C 
12.5 
12.2 
12.0 
13  0 

°F 
18 
20 
28 
28 

3.2 
2.6 
3.0 
2  9 

w  P  cor 
cor 
cor 

11.3 
5.9 
9.3 
8  3 

12  2 

c 

NE 

12  9 

30 

~2  5 

5  2 

1  9 

C 

NE 

13  4 

31 

2  9 

8.3 

16 

5.5 
9  6 

C 

c 

NE 
N 

13.5 
14  6 

30 
29 

4.3 
0  0 

wpg 

28.0 

o 

Snow  at  night. 

12  3 

c 

N 

14  4 

31 

2  3 

4.0 

3  2 

F 

NW 

15  3 

32 

2  7 

6  6 

4  5 

F 

NW 

15  5 

32 

2.8 

7  3 

5  4 

F 

NW 

15  4 

31 

3  2 

11  3 

7.1 

F 

NW 

15.9 

31 

2.7 

6.6 

9  2 

F 

NW 

15  9 

30 

2  4 

4  6 

10  6 

F 

NW 

16.3 

29 

2.9 

8.3 

17 

9  o 

F' 

NW 

13  9 

25 

2  4 

4  6 

10  8 

F 

NW 

13  8 

29 

3  0 

9  3 

12  1 

F 

NW 

15  5 

29 

3  3 

12  5 

q    O 

c 

NW 

16  6 

29 

3  4 

13.8 

4  2 

c 

N 

16  9 

29 

2.5 

5.2 

5  3 

c 

N 

16  8 

29 

2  7 

6  6 

18 

10  7 

C' 

NW 

14.0 

29 

2.7 

6.6 

Blizzard  at  night. 

19 

12.3 
1.1 
9  3 

C' 
C' 

c 

NW 
NW 
3 

14.0 
14.4 
13  6 

29 
30 
35 

3.7 
3.4 
2  7 

wbrg 
wrpg 

17.5 
13.8 
6  6 

12  6 

c 

s 

14  0 

41 

3  1 

10  2 

3  4 

c 

SW 

15  6 

41 

2.1 

2  7 

6  0 

c 

w 

16  2 

36 

2  7 

6  6 

20 

8  7 

F 

NW 

16  3 

31 

3  0 

9  3 

10  7 

F 

NW 

16  6 

32 

3  1 

10  2 

12  0 

F 

NW 

17  0 

32 

3.7 

17.5 

2  1 

F 

NW 

17  6 

32 

2  9 

8  3 

3  6 

F 

NW 

17  8 

32 

3.7 

17.5 

6  0 

C' 

W 

18  0 

32 

3  0 

9  3 

21 

9  1 

c 

W 

15  0 

31 

2  3 

4  o 

10  5 

C' 

NW 

15  3 

31 

3.2 

11  3 

12  2 

C' 

NW 

15  6 

31 

2  8 

7  3 

1  6 

F 

NW 

15  1 

30 

2.5 

5  2 

4  6 

F 

NW 

15  3 

26 

3  7 

17  5 

5  6 

F 

NW 

15  2 

25 

3  4 

13  8 

22 

8  9 

F 

SW 

13  7 

27 

2  4 

4  6 

30 

3  5 

F 

SW 

18  0 

30 

3  i 

10  2 

Snow  in  morning. 

5  7 

F 

SW 

18  0 

30 

2  8 

7.3 

Brass  trough. 

31 

9  4 

F 

SW 

17  8 

38 

1  9 

2  2 

10  8 

F 

SW 

18  8 

39 

2.4 

4.6 

12  1 

F 

SW 

18  8 

41 

2  3 

4  0 

3  3 

F 

SW 

19  4 

41 

2.2 

3.3 

5  8 

F 

SW 

19  8 

40 

2  4 

4  6 

1905. 
Tan      l 

10  5 

F 

w 

18  6 

40 

1  7 

1  8 

12  5 

F 

w 

19  3 

43 

2  7 

6  6 

2  6 

F 

w 

19  8 

45 

2  2 

q   q 

6  7 

F 

w 

20  0 

40 

1  9 

8  3 

2 

9  4 

C' 

SW 

18  4 

44 

0  0 

0  0 

10  6 

C' 

SW 

20  8 

43 

2.3 

4.0 

12  2 

c 

SW 

20  4 

44 

2  1 

2  7 

2  4 

c 

SW 

20  0 

43 

1  8 

1  9 

4  1 

c 

SW 

19  0 

42 

1  8 

1.9 

5  4 

c 

SW 

18  9 

42 

1  8 

1  9 

3 

8  6 

R 

NE 

17.4 

38 

0  0 

0  0 

10  0 

R 

NE 

17  8 

38 

0  0 

0  0 

12  2 

R 

NE 

17  8 

37 

0  0 

0  0 

2  8 

R 

NE 

17  3 

35 

0  0 

0  0 

5  0 

R 

N 

17  5 

32 

0  0 

0  0 

4 

9  7 

Sn 

N 

11  7 

17 

2  9 

8  3 

Blizzard,  60  miles. 

11  3 

C' 

NW 

12  0 

17 

1  9 

2  2 

12  3 

c 

NW 

12  4 

18 

2  8 

7.3 

5 

2.8 
5.2 
9.0 

C' 
F 
F 

NW 
NW 
SW 

12.8 
13.6 
12.2 

19 

17 
18 

2.1 
2.9 
2.3 



2.7 
8.3 
4.0 

NUCLEATION   AT   BLOCK  ISLAND. 


95 


TABLE  57. — Successive  observations  of  the  nucleation,  etc. — Continued. 


Date. 

1 

Weather. 

73 

a 
* 

Temperature 
of  appara- 
tus. 

Temperature 
of  atmos- 
phere. 

Aperture  s. 

Corona  col- 
ors. 

Number. 
n  X  10-8. 

Remarks. 

1905. 
Tan      5 

10  7 

F 

W 

°C 
13  0 

°F 
21 

2  8 

7  3 

12.3 

F 

w 

13  2 

25 

2.8 

7  3 

2  1 

F 

NW 

13  5 

25 

2  8 

7  3 

3  Q 

F 

NW 

13  8 

25 

4  3 

28  0 

4  9 

F 

NW 

13  9 

23 

2.9 

8  3 

5  8 

F 

NW 

13  9 

22 

2  0 

2  5 

6 

8  8 

Sn 

B 

13  9 

30 

0.0 

0  0 

10  1 

Sn 

E 

14  2 

32 

0  8 

8 

12  3 

Sn 

E 

14.7 

34 

1.0 

1.0 

3  3 

R 

E 

15  4 

36 

9  0 

g 

5  9 

c 

E 

15  8 

37 

1  0 

1  0 

Rain  at  night. 

7 

9  7 

c 

SE 

18  5 

49 

0  8 

8 

11  0 

c 

SE 

19  0 

50 

1  3 

1  3 

12  5 

F' 

sw 

19  5 

48 

1  5 

1  5 

3  5 

F 

sw 

20  0 

44 

1  7 

1  8 

5  9 

F 

sw 

19  7 

42 

1.8 

1.9 

g 

8  0 

F 

w 

14  4 

31 

1  6 

1  6 

1  5 

F 

w 

17  6 

33 

2  9 

8  3 

3  4 

F' 

w 

16  9 

33 

2  3 

4  0 

7  6 

F 

w 

16  9 

31 

2  0 

2  5 

g 

8  8 

F 

NW 

15  5 

28 

1  8 

1.9 

10  7 

F 

NW 

15  7 

29 

2  7 

6  6 

12  2 

F 

NW 

16  0 

30 

2  6 

5.9 

1  9 

F 

NW 

16  5 

31 

2  2 

3  3 

3  8 

F 

NW 

16  1 

31 

2  2 

3  3 

5  6 

C' 

NW 

16  1 

31 

1  8 

1  9 

10 

8  7 

c 

SW 

17  2 

36 

1  5 

1  5 

10  6 

C' 

w 

17  4 

36 

2  0 

2.5 

12  3 

C' 

w 

17  4 

37 

2  4 

4  6 

2  6 

<y 

w 

17  4 

36 

2  5 

5  2 

4°4 

F 

w 

17  4 

34 

2  7 

6  6 

5  3 

C' 

w 

17  5 

32 

3  4 

13  8 

U 

90 

c 

NW 

13  0 

25 

1  4 

1.4 

10  5 

F 

NW 

15  5 

26 

2  3 

4  0 

12  4 

c 

N 

16  0 

27 

2  1 

2.7 

3  1 

c 

NE 

16  5 

29 

2  3 

4  0 

4  9 

c 

NE 

17  1 

29 

2  7 

6  6 

5  g 

c 

NE 

17  0 

29 

3  3 

8.3 

12 

8  8 

R  Fog 

SE 

13  6 

41 

2  0 

2  5 

Do. 

10  7 

Fog 

sw 

15  7 

46 

2  3 

4.0 

12  5 

Fog  R 

sw 

16.7 

47 

1.5 

1.5 

2  4 

R  Fog 

SW 

17  8 

46 

1  8 

1.9 

3  4 

R 

SW 

18  2 

44 

1  8 

1.9 

5  6 

R  Fog 

sw 

18  8 

40 

1  8 

1.9 

13 

9.0 
11  6 

F 
C' 

NW 
NW 

16.9 
16.2 

29 

28 

1.8 
2  6 



1.9 

5.9 

Hazy. 

3  5 

c 

N 

16  4 

29 

2  8 

7.3 

5  7 

c 

N 

16  4 

28 

2  8 

7.3 

14 

9  5 

F 

N 

12  7 

19 

1  7 

1.8 

12  7 

F 

NW 

17  0 

22 

3  0 

9.3 

No  cloth  in  trough  from 

3  6 

F 

NW 

14  6 

22 

2  8 

7.3 

here  on. 

5  3 

F 

NW 

14  0 

21 

2  8 

7  3 

15 

8  4 

F 

NW 

11  5 

16 

2  2 

3.3 

11  0 

C' 

W 

12  1 

20 

2  5 

5  2 

12  8 

C' 

SW 

13  0 

21 

2  9 

8.3 

3  3 

C' 

w 

13  0 

23 

2  7 

6.6 

8  0 

F 

w 

14  0 

26 

3  3 

12.5 

16 

9  3 

F 

w 

13  7 

25 

3  6 

16.2 

Cleaned  trough. 

3  5 

F 

w 

15  0 

28 

3  2 

11.3 

4  9 

F 

w 

15  0 

28 

4  5 

32.4 

6  0 

F 

w 

15  0 

28 

3  7 

17.5 

8  1 

F 

w 

15  0 

27 

o   «> 

12  5 

9  6 

F 

w 

15  0 

27 

2  9 

8.3 

17 

9  0 

F 

w 

14  7 

30 

2  5 

5.2 

10.6 
12  5 

F 
F 

w 
w 

J5.7 
16  6 

32 
34 

3.3 
3  4 

12.5 
13.8 

3  2 

F 

w 

16  4 

34 

2  8 

7.3 

6  0 

F 

w 

14  1 

33 

2  6 

5  9 

18 

9.0 

F 

NW 

16.3 

32 

2.2 

3.3 

96         NUCLEATION   OF  THE  UNCONTAMINATED  ATMOSPHERE. 


TABLE  57. — Successive  observations  of  the  nucleation,  etc. — Continued. 


Date. 

ii 

8 
H 

Weather. 

1 

£ 

Temperature 
of  appara- 
tus. 

Temperature 
of  atmos- 
phere. 

Aperture  *. 

Corona  col- 
ors. 

Number. 
n  X  10-3. 

Remarks. 

1905. 
Tan    18 

10  5 

F 

NW 

°C 
16  4 

Ojf 

34 

2  7 

6  6 

12  0 

F 

NW 

16  5 

35 

2  9 

8.3 

3.0 

F 

NW 

17.2 

36 

2.5 

5.2 

4  6 

F 

NW 

17  5 

34 

2  7 

6.6 

19 

5.8 
8.8 
11.0 
12.4 

F 
F' 
F' 
F 

NW 
SW 
SW 
SW 

17.4 
16.5 
16.9 
17.0 

33 

40 
42 

42 

2.6 
1.9 
2.5 
3.1 

'.'.'.'.'.'.'.... 

5.9 
2.2 

5.2 
10.2 

2.4 

3  7 

F' 
F' 

SW 
SW 

17.6 
17  6 

39 
39 

2.7 
2  3 



6.6 

4.0 

6  0 

F' 

SW 

17.5 

39 

2.2 

3.3 

20 

9  1 

C' 

NW 

17  7 

37 

1  3 

1.3 

11  0 

C' 

NW 

17  8 

37 

2  5 

5  2 

12  5 

C' 

NW 

18  0 

40 

2  7 

6.6 

21 

3.2 
5.9 

9  0 

F 
F 
F 

NW 
NW 

NE 

18.4 
18.7 
14  7 

39 
36 
31 

3.1 
3.0 
1  9 



10.2 
9.3 
2  2 

12  2 

C' 

NE 

17  7 

34 

4.2 

25.8 

2  5 

c 

E 

16  9 

35 

3  5 

15.0 

5  1 

C 

SE 

16.9 

36 

3.1 

10.2 

Mist,  almost  rain. 

22 

9  0 

c 

s 

18  9 

40 

1  9 

2.2 

Ivight  rain,  almost  sun 

12  0 

c 

NW 

19  0 

38 

2.5 

5.2 

shine. 

1  5 

c 

NW 

19  3 

37 

2  5 

5  2 

4  0 

c 

NW 

19  0 

37 

2.1 

2.7 

7  5 

c 

NW 

18  7 

36 

1  8 

1.9 

23 

9  0 

F 

NW 

12.4 

19 

2.8 

7.3 

Cleaned  trough. 

12.2 
3  3 

F 

F 

NW 

NW 

14.7 
14.6 

21 
23 

4.2 
3.4 



25.8 
13.8 

6  1 

F 

NW 

14  3 

23 

3  1 

10.2 

24 

8.8 

F 

NE 

8.5 

20 

1.8 

1.9 

12.2 
2  8 

C' 
C 

NE 
NE 

11.0 
11.9 

23 

27 

2.4 
1.9 



4.6 
2.2 

5  7 

c 

E 

12  8 

29 

1  4 

1.4 

25 

8.9 

Sn 

NE 

12.0 

20 

1.9 

2.2 

Blizzard. 

11  8 

Sn 

NE 

10.8 

21 

2.8 

7.3 

Do. 

1.9 
5  1 

Sn 
Sn 

NE 
N 

10.5 
10  5 

22 

12 

2.6 
2  5 



5.9 
5.2 

Do. 
Do. 

26 

9  0 

F 

NW 

8  6 

10 

2.4 

4.6 

10  8 

F 

NW 

8  6 

12 

3  0 

9.3 

12  6 

F' 

NW 

8  5 

14 

3  2 

11.3 

3  2 

F' 

NW 

8  5 

14 

3  1 

10.2 

5  6 

F 

NW 

8  5 

22 

3  0 

9  3 

27 

8.8 
12  3 

F 
F 

W 

w 

10.0 
11.7 

18 
22 

2.9 
4.0 



8.3 
22.0 

3  3 

F' 

SW 

12  8 

24 

3  9 

20.5 

5  5 

F' 

SW 

13  0 

26 

3  3 

12.5 

28 

9.3 
12  0 

Sn 

c 

SW 
SW 

14.6 
15  4 

29 
34 

2.8 
2  9 



7.3 

8.3 

3  1 

C' 

w 

15  6 

33 

2.1 

2.7 

5  7 

C' 

w 

15  6 

30 

4  1 

24.0 

29 

9  3 

F 

NW 

13  6 

19 

1  9 

2.2 

12  0 

F 

NW 

14  6 

21 

2  1 

2.7 

1  7 

F 

NW 

14  7 

24 

2  6 

5.9 

3  1 

F 

SW 

15  0 

24 

3  2 

11.3 

30 

9  2 

Sn 

N 

15  0 

20 

1.9 

2.2 

12.3 

o   q 

Sn 
Sn 

NE 
NE 

14.7 
14  8 

22 

24 

2.9 
3.1 



8.3 
10.2 

5   4 

c 

NE 

13  9 

23 

3  6 

16.2 

31 

8.9 
12  3 

C' 

c 

NE 

NE 

12.7 
13.5 

17 
22 

1.4 
2.6 

1.4 
5.9 

2  8 

C' 

NE 

13  7 

23 

3  2 

11.3 

5  6 

C' 

NE 

13.6 

22 

3.4 

13.8 

Feb     1 

9  0 

F 

NW 

14  0 

19 

2  6 

5.9 

12  4 

F 

NW 

15.6 

24 

4.3 

28.0 

3  0 

C' 

W 

15  3 

26 

3  6 

16.2 

5  7 

c 

SW 

15  1 

26 

3  4 

13.8 

2 

9  0 

C' 

NW 

12.2 

22 

3  1 

10.2 

Snow  at  night. 

12  3 

c 

NW 

14  0 

22 

4  i 

24.0 

2.3 

C' 

NW 

13.9 

21 

4.6 

34.8 

NUCLEATION   AT   BLOCK   ISLAND. 


97 


TABLE  57. — Successive  observations  of  the  nucleation,  etc. — Continued. 


Date. 

! 

H 

Weather. 

i 

'§• 

Temperature 
of  appara- 
tus. 

Temperature 
of  atmos- 
phere. 

Aperture  s. 

Corona  col- 
ors. 

i 

tix 

T 

i 

Remarks. 

1905. 
Feb      2 

5  4 

C' 

NW 

°C 
15  0 

°F 
19 

4.6 

34.8 

3 

9  0 

C' 

NW 

10  0 

9 

3.7 

17.5 

10  5 

C' 

NW 

10  0 

11 

4.8 

39.5 

12.2 
3  0 

F 

F 

NW 

NW 

10.0 
11  6 

15 

19 

5.1 

4.7 



46.0 
37.2 

6  2 

F 

NW 

12  9 

17 

3.7 

17.5 

4 

9  5 

F 

NW 

10.0 

10 

4.0 

22.0 

10  7 

F 

NW 

10  0 

12 

4.2 

25.8 

12  2 

F 

NW 

10  0 

14 

4  7 

37  2 

3  0 

F 

NW 

11  9 

16 

4.5 

32.4 

6  3 

F 

NW 

11  6 

16 

3  7 

17.5 

5 

8  4 

F 

N 

12  0 

14 

2.5 

5.2 

10.0 
1  3 

F 
F 

irk 

NE 

12.0 
13  6 

18 
24 

3.9 
3  fi 



20.5 
16.2 

3  3 

F 

E 

15  3 

24 

3.0 

9.3 

6  3 

F 

E 

15  4 

24 

3  7 

17.5 

Snow  at  night. 

6 

9  4 

R 

E 

13  8 

32 

0.0 

0.0 

Cleaning  apparatus. 

7 

6.0 
9  3 

Fog 

NW 

NW 

17.4 
14  7 

33 
22 

2.1 
4  2 



2.7 

25.8 

Mending  apparatus. 

3  7 

F 

NW 

14  1 

23 

4  7 

37.2 

6  2 

F 

NW 

13  6 

21 

3  R 

16.2 

g 

9  2 

F 

NW 

11  4 

16 

3  9 

20.5 

12  5 

F 

NW 

12  6 

26 

4.0 

22.0 

2  6 

F 

NE 

13  6 

30 

3  6 

16.2 

5  7 

F 

w 

14  0 

27 

4  1 

24.0 

g 

9  3 

Sn 

E 

14  6 

30 

1.3 

1.3 

Snow  at  night. 

12  5 

R 

E 

15  5 

33 

2  0 

2.5 

3  3 

R 

E 

13  7 

33 

0.0 

0.0 

5  8 

R 

E 

15  5 

33 

0  8 

0.8 

10 

9  2 

c 

W 

17  0 

32 

3  6 

16.2 

12  4 

C' 

sw 

18  0 

34 

4  4 

30.0 

3  1 

c 

w 

17  5 

34 

3  2 

11.3 

5  8 

F 

w 

17  5 

32 

2.7 

6.6 

11 

9  4 

F 

NW 

13  6 

21 

3  0 

9.3 

12  2 

F 

NW 

13  7 

23 

4.9 

41.7 

3  5 

F 

W 

14  1 

24 

4  3 

28.0 

5  8 

F 

W 

14.2 

23 

3.9 

20.5 

12 

8  5 

F 

SE 

14  3 

25 

2  7 

6.6 

11  5 

c 

SE 

14  8 

29 

2  9 

8.3 

1  0 

c 

SE 

15  7 

31 

2.5 

5.2 

30 

c 

SE 

16  0 

34 

2  7 

6.6 

6  4 

R 

SE 

16  4 

37 

2.7 

6.6 

13 

9  1 

c 

sw 

17  0 

35 

2  9 

8.3 

Rain  at  night. 

10  8 

R 

sw 

17  0 

36 

2.6 

5.9 

12  5 

R 

w 

16  4 

35 

2  7 

6.6 

30 

Sn 

NW 

16  4 

28 

2  7 

6.6 

5  8 

c 

NW 

15  8 

25 

2  9 

8.3 

14 

9  4 

F 

W 

12  1 

13 

4  3 

28.0 

in    q 

F 

w 

11  0 

15 

3  7 

17.5 

2  5 

F 

sw 

11  0 

16 

3  8 

19.0 

ft  ft 

F 

sw 

12  7 

17 

3  8 

19.0 

15 

9  3 

c 

E 

11  4 

24 

1  8 

1.8 

Ho 

c 

E 

12  7 

24 

2  2 

3.3 

UQ 

c 

E 

12  7 

24 

2  0 

2  5 

3C 

Sn 

NW 

13  5 

24 

3  3 

12.5 

5  7 

C' 

NW 

14  3 

23 

3  1 

10.2 

16 

94. 

F 

NW 

10  0 

10 

5  9 

68.0 

in    n 

F 

NW 

10  0 

14 

5  1 

46.0 

3    3 

F 

NW 

11  5 

17 

4  8 

39.5 

5  a 

F 

NW 

12  6 

17 

3  9 

20.5 

17 

9  4 

c 

SW 

12  8 

32 

2  7 

6.6 

in   n 

C' 

sw 

13  7 

36 

2  6 

5.9 

Q 

SW 

15  0 

32 

2  7 

6.6 

5c 

c 

sw 

15  8 

31 

2  8 

7.3 

in 

F 

w 

13  9 

21 

3  6 

16.2 

F' 

w 

13  9 

22 

4  4 

30.0 

3    A 

F' 

w 

14  1 

22 

3  g 

19.0 

F' 

NW 

14  0 

20 

3  6 

16.2 

19 

8.6 

12  3 

F' 
F' 

NW 
W 

11.7 
12.9 

15 

18 

2.9 
3.7 



8.3 
20.5 

98         NUCLEATION   OF  THE  UNCONTAMINATED   ATMOSPHERE. 


TABLE  57. — Successive  observations  of  the  nucleation,  etc. — Continued. 


Date. 

| 

Weather. 

i 

% 

Temperature 
of  appara- 
tus. 

Temperature 
of  atmos- 
phere. 

Aperture  s. 

Corona  col- 
ors. 

Number. 
n  X  10-3. 

Remarks. 

1905. 
Feb    19 

3  8 

F' 

w 

°C 
13  9 

op 

21 

4  2 

25  8 

Aspirator  hereafter. 

6  5 

F' 

w 

13  8 

21 

3  6 

16  2 

20 

9  i 

c 

sw 

14  9 

33 

2  4 

4  6 

12  3 

Sn 

sw 

15  4 

31 

3  1 

10  2 

3  0 

Sn 

sw 

15  6 

32 

3  0 

9  3 

5  4 

c 

sw 

17  0 

32 

3  3 

12  5 

21 

9  2 

F 

NW 

18  2 

35 

2.9 

o   o 

Rain  at  night. 

12  0 

F 

NE 

18  3 

38 

3  2 

11  3 

4  3 

F 

E 

18  8 

36 

7 

1  8 

6  0 

F 

E 

18  9 

35 

.5 

1.5 

22 

9  1 

c 

NE 

17  3 

31 

o 

1  0 

11  0 

c 

NE 

17  0 

31 

2 

1  2 

12  3 

c 

NE 

16  9 

30 

4 

1.4 

30 

c 

NE 

16  6 

30 

0  8 

0  8 

6  0 

c 

NE 

16  4 

30 

0  0 

0  0 

23 

9  3 

C' 

N 

11  7 

23 

2  6 

5  9 

12  0 

C' 

N 

12  6 

25 

4  5 

32.4 

2  2 

C' 

NE 

13  4 

29 

4  6 

34  8 

4  6 

F 

NE 

14  5 

32 

4.0 

22.0 

5  8 

F 

NE 

14  8 

31 

3  6 

16  2 

24 

8  8 

F' 

N 

14  9 

28 

2.3 

4.0 

12  2 

F' 

N 

15  0 

35 

3  9 

20.5 

3  0 

F' 

NW 

15  8 

36 

4.6 

34.8 

25 

6.0 
8.9 

F' 
F 

NW 
NW 

15.8 
17  0 

35 
27 

3.4 
2.6 



13.8 
5.9 

12  3 

F 

W 

17  5 

32 

4  2 

25.8 

2  9 

F 

W 

18  0 

35 

3  4 

13  8 

5  8 

F 

W 

18  3 

31 

3.1 

10.2 

26 

8  7 

c 

NE 

18  2 

33 

2  4 

4  6 

12  1 

c 

N 

17  5 

32 

2.6 

5.9 

3  1 

c 

NW 

18  2 

34 

3  0 

9  3 

6  3 

F' 

W 

18  4 

35 

3.4 

13.8 

27 

9  1 

F 

W 

14  0 

22 

3  8 

19  0 

12.1 

F 

W 

14  5 

25 

4.2 

25.8 

3  2 

F' 

W 

15  0 

25 

4.2 

25.8 

5  8 

F' 

w 

15  5 

26 

3  7 

17  5 

28 

9  0 

F' 

w 

15  2 

31 

3.9 

20.5 

12  2 

F' 

sw 

15  4 

35 

3  0 

9  3 

3.3 
6  0 

F' 
F' 

sw 
w 

15.7 
17  0 

34 
32 

3.0 

4.0 



9.3 
22.0 

Mar.   l 

9,2 
12  0 

F' 
F' 

NW 
W 

15.7 
16  3 

25 

28 

5.1 
4.1 

w|b|p 

46.0 
24.0 

3  1 

F 

w 

17  0 

29 

4  4 

30.0 

6  0 

F 

w 

17.7 

28 

3.6 

16.2 

2 

9  2 

F 

w 

14  4 

20 

4  4 

30.0 

12  0 

F 

w 

13  0 

24 

4  0 

22  0 

3  1 

F 

w 

12  4 

27 

4.7 

37.2 

6  0 

F 

w 

13  4 

28 

3  7 

17  5 

3 

9  0 

F 

NW 

15  2 

24 

4.0 

22.0 

12  2 

F 

NW 

15  8 

29 

4  2 

25.8 

3  4 

F 

W 

16  4 

31 

3.5 

15.0 

6  0 

F 

W 

17  0 

30 

3  8 

19.0 

4 

9  2 

c 

s 

13  2 

34 

4  0 

22.0 

12  2 

c 

s 

15  0 

34 

3.1 

10.2 

3  0 

c 

{*} 

16  9 

37 

2.3 

4.0 

5  8 

c 

1  N  J 

N 

17.4 

35 

2.2 

3.3 

5 

8  8 

F 

NW 

13  9 

19 

2.1 

2.7 

12  2 

F 

s 

15  0 

24 

3  5 

15  0 

3  5 

c 

SW 

15.8 

25 

3  2 

11.3 

6  2 

F 

sw 

16  0 

26 

2  9 

8  3 

6 

9  0 

F 

N 

15.5 

37 

9  3 

4.0 

12  3 

F 

N 

16  0 

31 

3  1 

10.2 

7 

3.2 
5.6 
8  9 

F 
F 
C' 

W 

w 

s 

16.6 
17.1 
17  4 

33 
31 
34 

3.9 
3.7 
3  5 



20.5 
17.5 
15.0 

12  3 

c 

s 

17.6 

34 

3.1 

10.2 

2  8 

c 

s 

18  3 

35 

2  6 

5.9 

6  0 

Sn 

SE 

18.4 

33 

2.6 

5.9 

8 

9.0 

Foe 

SW 

18.0 

35 

2.4 

4.6 

Rain  at  night. 

NUCLEATION   AT   BLOCK  ISLAND. 


99 


TABLE  57. — Successive  observations  of  the  nucleation,  etc.— Continued. 


Date. 

<u 

s 

h 

Weather. 

| 

§ 

Temperature 
of  appara- 
tus. 

Temperature 
of  atmos- 
phere. 

Aperture  *. 

Corona  col- 
ors. 

t 

S'x 

T 

Remarks. 

1905- 
Mar.    8 

11.9 

Fog 

SW 

°C 
18  1 

op 
35 

2  5 

5  2 

3.6 

Fog 

sw 

18.1 

34 

3.0 

9.3 

5.7 

Fog 

sw 

18.3 

34 

2.6 

5  9 

9 

9.0 

F 

w 

19.0 

35 

3.0 

9.3 

Rain  at  night. 

12.5 

c 

sw 

18.6 

38 

2  5 

5.2 

3  3 

c 

SE 

17  6 

37 

2  6 

5  g 

5.9 

R 

sw 

17.3 

34 

2.5 

5.2 

10 

9  0 

c 

N 

18  8 

36 

2  7 

6  6 

Do 

12.1 

C 

NW 

19.3 

37 

2.8 

7.3 

3.2 

F' 

W 

19  7 

37 

2  4 

4  6 

Clearing 

6.0 

F' 

w 

20.0 

34 

S  3 

12.5 

11 
12 

9.0 
12.0 
3.1 
6.0 
9.0 

F 
F 
F 
F 
F' 

NW 

NW 
W 
W 

sw 

15.0 
15.6 
16.4 
17.0 
17.0 

28 
30 
31 
30 
35 

3.5 
4.3 
4.6 
3.9 
3  4 

wrg 
wrg 
w  r  p 
wrg 

15.0 
28.0 
34.8 
20.5 
13.8 

12  1 

C 

sw 

17  4 

37 

3  1 

10  2 

3.0 

C 

sw 

18.0 

36 

3.1 

10.2 

8  2 

F' 

sw 

18  3 

33 

2  5 

5.2 

13 

9.1 
12.1 

F' 
F 

N 
NE 

14.7 
15.8 

27 
30 

3.1 
3  6 

10.2 
16.2 

3.2 

F 

SW 

16.6 

32 

8  6 

16.2 

6.1 

F 

SW 

17.0 

29 

2.9 

8.3 

14 

9.0 

F 

N 

17.4 

31 

?  9 

8.3 

15 

12.1 
3.2 
5.9 
9.3 
12-4 

C' 
F 
F 
F 
F 

NE 
SW 
NW 
NE 
SW 

17.5 
18.2 
18.5 
15.5 
16.8 

34 
36 
32 
28 
34 

3.4 
3.5 
3.1 
3.4 
9  9 

wrg 
wrg 

w  rb  p 

13.8 
15.0 
10.2 
13.8 
8.3 

16 
17 

18 

2.9 
6.0 
9.3 
12.3 
2.6 
5.7 
8.8 
12.1 
2.6 
6.0 
9.0 
12.1 
3.0 
6.0 

F 
F 
F 
F 
C 
C 
C 
F 
F 
F 
C' 
C' 
C' 
F 

SW 

sw 
w 
sw 
sw 
sw 
NE 
E 
SE 

s 
sw 
sw 
sw 
sw 

16.8 
18.0 
17.9 
18.3 
18.8 
18.7 
18.5 
18.6 
19.4 
19.0 
17.5 
17.5 
18.3 
18.0 

34 
30 
33 
39 
36 
36 
33 
37 
39 
33 
42 
47 
45 
44 

3.3 
3.7 
3.6 
3.0 
2.4 
2.1 
2.9 
3.1 
2.6 
2.8 
3.1 
2.5 
2.4 
2.4 

w  bp 
w  ro  g 
wbrb 
w|b|p 
cor 
cor 
cor 
w|b|p 
cor 
cor 
cor 
cor 

12.5 
17.5 
16.2 
9.3 
4.6 
2.7 
8.3 
10.2 
5.9 
7.3 
10.2 
5.2 
4.6 
4.6 

Haze. 

19 

8.8 
12  1 

R 
R 

sw 
sw 

14.8 
16  2 

42 
42 

2.2 
2  6 



3.3 
5.9 

20 

3.6 
6.3 

8.8 
12  0 

R 

Fog 
RFog 

c 

w 

w 

NE 
NE 

18.9 
18.5 
14.7 
15.2 

42 
40 
34 
35 

3.1 
2.4 
1.0 
1  4 

w  b  p 
cor 
cor 

10.2 
4.6 
1.0 
1.4 

3  4 

Foe 

NE 

16  2 

34 

1  6 

1.6 

6  2 

c 

NE 

16-4 

33 

1  9 

2.2 

21 

9  3 

R 

NE 

16  1 

34 

1  0 

1.0 

12  1 

R 

NE 

15.8 

34 

1.3 

1.3 

2  8 

R 

NE 

15  6 

33 

1  1 

1.1 

5  7 

R 

NE 

15.4 

33 

1.0 

1.0 

22 

9.0 
12.5 
3.0 
6  0 

C 

C 
C 
F 

NE 
NE 
NE 
E 

12.0 
13.7 
14.0 
15  4 

33 
35 
36 
35 

2.9 
2.9 
2.5 
2  1 

cor 
w|b|r 
cor 

8.3 
8.3 
5.2 
2  7 

23 

9  0 

F 

NE 

15.0 

35 

2  6 

5.9 

12  0 

F 

E 

16  5 

36 

1  9 

2.2 

3  0 

F 

SE 

17.5 

37 

1.6 

1.6 

24 
25 

5.8 
9.0 
12.2 
3.0 
5.9 
9.0 
12.3 
3.0 

F 
C 
Fog 

C 

Fog 
Fog 
Fog 

SE 
E 
S 
E 
E 
S 

sw 
sw 

16.7 
17.0 
18.0 
18.0 
18.0 
20.0 
20.0 
20.0 

36 
36 
39 
40 
39 
43 
42 
42 

2.0 
1.4 
1.7 
1.9 
1.5 
1.9 
2.4 
2.7 

cor 
cor 
cor 
cor 
cor 
cor 
cor 
cor 

2.5 

1     4 

1.8 
2.2 
1.5 
2.2 
4.6 
6.6 

100      NUCLEATION   OF  THE   UNCONTAMINATED  ATMOSPHERE. 


TABLE  57. — Successive  observations  of  the  nucleation,  etc. — Continued. 


Date. 

Time. 

Weather. 

Wind. 

Temperature 
of  appara- 
tus. 

Temperature 
of  atmos- 
phere. 

Aperture  s. 

Corona  col- 
ors. 

Number. 
n  x  10-3. 

Remarks. 

1905- 

°C 

OF 

Mar.  25 

5.8 

R 

NW 

20.0 

40 

2.1 

cor 

2.7 

26 

8.9 

F 

W 

20.0 

43 

3.3 

w    b|p 

12.5 

Rain  at  night. 

12.0 

F 

W 

20.0 

50 

3.2 

w    b|p 

11.3 

3.1 

F 

SW 

21.0 

48 

2.6 

cor 

5.9 

6.3 

F 

S 

21.0 

40 

2.7 

cor 

6.6 

27 

9.0 

F 

SW 

19.0 

43 

1.8 

cor 

1.9 

12.3 

F' 

SW 

18.0 

48 

2.2 

cor 

3.3 

3.0 

F' 

W 

19.0 

49 

2.4 

cor 

4.6 

6.1 

F 

SW 

18.0 

45 

2.5 

cor 

5.2 

28 

9.3 

F 

W 

19.0 

47 

2.6 

cor 

5.9 

12.0 

F' 

SW 

19.0 

52 

2.6 

cor 

5.9 

3.0 

F' 

SW 

19.0 

55 

2.3 

cor 

4.0 

6.0 

F 

SW 

19.0 

49 

2.0 

cor 

2.5 

29 

9.3 

F 

E 

21.0 

43 

.3 

cor 

.3 

12.2 

F 

E 

22.0 

44 

.3 

cor 

.3 

3.0 

F 

E 

22.0 

43 

.1 

cor 

.1 

6.0 

F 

E 

20.0 

40 

.2 

cor 

.2 

30 

9.0 

F  Fog 

E 

19.0 

41 

.0 

cor 

.0 

Fog  at  night. 

12.0 

F' 

s 

20.0 

47 

.2 

cor 

.2 

2.5 

F'Fog 

SW 

20.0 

45 

1.2 

cor 

.2 

6.0 

F' 

SW 

19.0 

46 

1.0 

cor 

1.0 

31 

8.7 

F 

W 

16.0 

45 

2.3 

cor 

4.0 

Rain  at  night. 

12.0 

F 

W 

19.0 

52 

3.1 

w    b    P 

10.2 

3.0 

F 

W 

20.0 

52 

2.5 

cor 

5.2 

6.0 

F 

SW 

21.0 

49 

2.6 

cor 

5.9 

Apr.     1 

9.0 

F 

NW 

18.0 

45 

2.3 

cor 

4.0 

12.0 

F 

NW 

17.0 

48 

3.6 

w  br  bg 

16.2 

3.0 

F 

NW 

18.0 

47 

2.8 

cor 

7.3 

5.8 

F 

NW 

19.0 

45 

3.0 

w|b|p 

9.3 

2 

9.2 

F 

NW 

16.0 

35 

1.9 

cor 

2.2 

12.0 

F 

NW 

16.0 

40 

2.0 

cor 

2.5 

2.5 

F 

NW 

17.0 

43 

2.1 

cor 

2.7 

6.1 

F 

N 

18.0 

41 

2.5 

cor 

5.2 

3 

9.0 

F 

NW 

18.0 

38 

3.4 

w  bp 

13.8 

12.0 

F 

NW 

19.0 

46 

3.6 

w  ro  bg 

16.2 

3.0 

C' 

W 

19.0 

51 

3.0 

w    b    p 

9.3 

6.0 

C' 

W 

18.0 

48 

3.0 

w    b    p 

9.3 

4 

9.0 

CFog 

SE 

20.0 

41 

2.5 

cor 

5.2 

12.1 

C 

SE 

20.0 

43 

2.0 

cor 

2.5 

3.0 

C 

SE 

20.0 

42 

2.3 

cor 

4.0 

6.0 

C 

SE 

20.0 

42 

1.8 

cor 

1.9 

5 

9.0 

CFog 

NE 

20.0 

41 

2.1 

cor 

2.7 

Rain  and  thaw  at  night. 

12.1 

Fog 

N 

20.0 

43 

1.9 

cor 

2.2 

3.0 

Feg 

E 

19.0 

42 

2.2 

cor 

3.3 

5.9 

Fog 

NE 

18.0 

41 

2.2 

cor 

3.3 

6 

9.0 

CFog 

S 

20.0 

47 

1.6 

cor 

1.6 

Do. 

12.1 

Fog 

SW 

20.0 

44 

1.9 

cor 

2.2 

3.0 

C 

SW 

19.0 

42 

3.3 

w  bp 

12.5 

6.0 

F 

W 

18.0 

42 

1  8 

cor 

1.9 

7 

9.0 

F 

W 

14.0 

39 

2.3 

cor 

4.0 

Cleaned  flue  in  morning. 

12.0 

12.2 
3.0 
6.0 

F' 

F' 
F' 
F' 

W 

W 
W 
W 

13.0 

13.0 
17.0 
18.0 

42 

42 
44 
40 

4.9 

5.7 
2.9 
3.0 

w  b  p 
w  cr  g 
w    bfp 
w    b|p 

41.7 

61.5 
8.3 
9.3 

f  Test  in  afternoon  show- 
j   ed  that  this  did  not  pro- 
's duce    maximum.     No 
I.  steamers  in  harbor. 

8 

8.6 

F' 

W 

19.0 

38 

2.7 

cor 

6.6 

12.3 

F' 

W 

19.0 

43 

3.1 

w  b  p 

10.2 

3.1 

F' 

W 

20.0 

43 

2.9 

cor 

8.3 

6.0 

F' 

W 

20.0 

40 

2.2 

cor 

3.3 

9 

9.3 

F 

W 

18.0 

41 

2.8 

cor 

7.3 

12.0 

C' 

W 

19.0 

45 

3.0 

cor 

9.3 

3.0 

C' 

SW 

19.0 

45 

2.9 

cor 

8.3 

6.3 

C' 

SW 

17.0 

41 

1.9 

cor 

2.2 

10 

8.5 

C' 

SW 

13.0 

46 

2.2 

cor 

3.3 

12.1 

C 

SW 

16.0 

49 

2.1 

cor 

2.7 

3.0 

C' 

SW 

19.0 

51 

2.1 

cor 

2.7 

6.0 

C 

SW 

20.0 

48 

1.3 

cor 

1.3 

11 

9.3 

RFog 

SW 

18.0 

2.2 

cor 

3.3 

12.6 

Fog 

NE 

17.0 

— 

1.5 

cor 

1.5 

4.0 

Fog 

NE 

17.0 

— 

1.4 

cor 

1.4 

6.2 

RFog 

NE 

16.0 

~~ 

1.6 

cor 

1.6 

NUCLEATION   AT   BLOCK  ISLAND.  IOI 

76.  Observations.— In  the  data  as  given  in  table  57,  the  first  column 
contains  the  date  and  daily  average  ;  the  second  and  third,  the  time  in 
twentieths  of  a  day  and  hours  ;  the  fourth  shows  the  condition  of  wind 
and  weather,  R  denoting  rain,  Sn  snow,  H  haze,  S  sun,  F  fair,  Fc 
or  F'  or  C'  partly  cloudy,  C  cloudy.  The  fifth  column  shows  the 
temperature  of  the  instrument  in  degrees  Centigrade,  and  the  sixth, 
the  temperature  of  the  outside  air  in  Fahrenheit  degrees.  Column 
8  shows  the  aperture  of  the  corona  on  the  given  goniometer:  9,  the 
principal  colors  from  the  center  outward ;  10  (from  March  29),  the 
relative  humidity  and  vapor  pressure ;  finally,  the  last  column  gives 
the  nucleation  in  thousands  of  nuclei  per  cubic  centimeter. 

It  will  be  noticed  that  the  temperature  of  the  air  in  the  trough  varies 
considerably  at  times  from  20°  C.,  the  temperature  for  which  reduc- 
tions were  made.  Each  reading  was  later  corrected  and  the  results 
thus  obtained  plotted,  where  the  correction  amounted  to  more  than  a 
thousand.  The  corrections  as  a  rule  were  not  large,  however,  and 
the  original  curve  shows  the  relative  values  equally  well.  The  chief 
effect  is  a  slight  reduction  of  the  maxima  on  cold  days. 

In  the  plates  of  the  next  chapter  (figs.  95-101)  the  individual  obser- 
vations are  plotted  with  the  weather  and  mean  temperature,  the 
nucleation  being  given  in  thousands  of  nuclei  per  cubic  centimeter. 
The  lower  curve  belongs  to  Block  Island,  the  upper  curve  to  Provi- 
dence, as  will  there  be  specified. 

ft.  Remarks  on  the  tables  (wood  fog  chamber).— With  the  beginning 
of  observations  at  the  island,  there  is  a  marked  drop  from  the  high 
readings  taken  in  Providence,  showing  that  a  large  part  of  the  nuclea- 
tion observed  in  the  latter  place  is  due  to  local  effects.  The  same 
variations  with  meteorological  changes  are,  however,  observed,  per- 
haps even  more  strikingly.  Thus  one  may  note  the  sudden  rise  in  the 
afternoon  of  November  27,  when  the  sky  cleared  and  the  wind 
changed  to  northwest.  On  the  3oth  the  rain  of  the  preceding  night 
is  followed  by  a  minimum,  which,  owing  to  cloudy  weather,  lasts 
several  days.  Snow  from  the  east  and  south  on  December  5  cuts 
down  the  nucleation,  which  rises  again  with  the  clear  sky  and  north- 
west wind  of  the  6th  (note  the  midday  minimum)  and  holds  during  the 
two  cloudy  but  dry  days  following.  The  clear  weather  and  northwest 
winds  of  the  9th,  nth,  and  i4th  bring  decided  maxima,  while  minima 
accompany  the  northeast  wind  and  cloudiness  of  the  loth,  and  the 
snow  from  the  same  quarter  on  the  i2th  and  i3th.  Midday  minima 
occur  again  on  the  i5th  and  i6th  ;  the  high  reading  late  in  the  after- 
noon of  the  1 5th  is  unusual.  The  i6th  shows  the  increase  of  nuclea- 


103      NUCLEATION   OF  THE  UNCONTAMINATED  ATMOSPHERE. 

tion  with  clear  northwest  wind,  while  the  following  day  (i7th)  well 
illustrates  the  effect  of  clouds  and  northeast  wind.  It  is  interesting  to 
note  that  the  blizzard  and  snow  produced  no  further  diminution.  On 
the  2Oth  another  midday  minimum  occurs,  with  a  clear  west  wind  all 
day.  The  2ist  shows  the  rise  due  to  clearing  sky. 

?8.  Remarks  on  the  tables  (brass  fog  chamber).— The  observations 
were  interrupted  from  the  22d  to  the  2gth  on  account  of  some  needed 
repairs,  and  after  that  date  the  brass  trough  replaced  the  wooden  one 
previously  used.  With  the  low  nucleations  frequently  found,  a  fog 
chamber  rigorously  free  from  leaks  is  essential. 

During  January,  maxima,  usually  accompanying  clear  weather  and 
west  to  north  wind,  occur  on  the  5th,  loth,  i6th,  23d,  and  27th  to 
28th ;  minima  due  to  rain  or  snow,  with  wind  from  the  opposite 
quarter,  appear  on  the  3d,  6th,  i2th.  22d,  and  24th  to  25th.  On  the 
4th,  the  notched  minimum  is  uncommon,  for  the  weather  at  the  sev- 
eral times  of  observations  is  •  ^  ^  \^  *Q  .  The  5th  shows  a 
high  reading,  as  the  wind  passes  through  the  northwest,  and  the  nth 
a  sun  and  cloud  effect.  One  may  notice  a  curious  gradual  decrease 
on  the  1 6th,  iyth,  and  i8th,  with  continual  clear  weather  and  westerly 
wind.  Clouds  on  the  morning  of  the  2oth  bring  the  maximum  later 
in  the  day,  and  the  next  day  (2ist)  shows  an  unusual  maximum,  with 
cloudy  sky  and  northeast  wind. 

During  January  and  February  there  is  a  noticeable  tendency  to  a 
uniform  type  of  day  curve,  rising  rather  steeply  from  9  o'clock  until 
noon  or  later,  and  falling  more  gradually  during  the  afternoon  and 
evening.  This  is  what  one  would  expect  on  sunny  days,  in  view  of 
the  fact  that  nuclei  seem  to  persist  for  some  time  in  the  atmosphere. 
This  curve  is  quite  well  shown  on  the  lyth,  i8th,  and  igih. 

In  February  the  maxima  are  higher,  and  occur  on  the  ist  to  5th, 
yth  to  8th,  loth  to  nth,  i4th,  i8th  to  igth,  23d  to  25th,  and  27th  to 
28th.  On  the  6th,  9th,  I2th  to  i3th,  and  2oth  we  have  rain  minima, 
and  low  readings  due  to  clouds  on  the  i5th,  i7th,  and  26th.  The  8th 
shows  an  interesting  minimum  during  a  temporary  shift  of  the  wind 
to  northeast,  and  the  i3th  a  depression  during  the  rain  in  the  middle 
of  the  day.  Clearing  weather  on  the  afternoon  of  the  I5th  brings  a 
rise  of  nucleation,  which  attains  an  unusual  value  next  day.  A  quick 
drop  occurs  on  the  2ist  when  the  wind  changes  to  east,  and  the 
opposite  effect  appears  on  the  26th.  Another  curious  midday  mini- 
mum may  be  noticed  on  the  28th.  Throughout  the  month  the  minima 
are  very  quickly  established  by  clear  weather  and  northwest  wind. 


NUCLEATION   AT   BLOCK   ISLAND.  103 

In  March  the  maxima  are  less  pronounced ;  they  occur  on  the  ist 
to  3d,  nth,  i3th  to  i6th,  and  26th.  Minima  of  longer  duration  than 
heretofore  accompany  the  rains  of  yth  to  loth,  igth  to  2ist,  23d  to 
25th,  and  2gth  to  31  St.  One  may  note  the  midday  minima  on  the  ut, 
2d,  and  3d.  The  4th  shows  a  reversal  of  the  usual  agreement  between 
the  wind  and  nucleation.  On  the  yth  the  readings  fall  during  the 
day  as  rain  sets  in.  The  wind  on  the  i3th,  i4th,  and  15th  changes 
suddenly,  near  noon,  from  northeast  to  southwest,  but  no  definite 
corresponding  change  appears  in  the  nucleation.  A  fine  cloud  effect 
is  shown  on  the  1 6th  when  the  sky  becomes  overcast  in  the  afternoon . 
On  the  23d  one  may  note  a  minimum,  as  the  wind  passes  through  the 
east  to  south. 

The  variations  in  the  nucleation  in  April  are  even  less  marked  ;  low 
maxima  occur  on  the  ist,  3d,  yth,  and  i4th  to  i6th,  while  minima 
accompany  rain  and  fog  on  the  4th  to  6th,  and  loth  to  i4th.  An 
unusually  low  value  is  obtained  on  the  2d,  with  clear  northwest  wind, 
and  on  the  yth  is  an  unaccountable  high  reading  which  seems  to  have 
no  connection  with  local  influences.  From  the  i6th  the  weather  is 
warm,  with  considerable  fog,  and  the  nucleation  runs  low,  with  little 
variation  to  the  end  of  the  month. 

79.  Summary  and  comparisons. — In  figures  91  and  92  are  shown 
together  the  current  nucleations  (continuous  heavy  black  line),  sun- 
shine (continuous  light  black  line),  vapor  pressure  (heavy  broken 
line),  temperature  (light  broken  line),  and  general  weather  conditions 
for  each  day.  The  nucleation  and  temperature  given  is  the  average 
of  the  observations  taken  during  the  day,  as  is  the  vapor  pressure 
after  March  28th  ;  before  that  date  the  vapor  pressure  is  the  mean  of 
the  regular  morning  and  evening  observations  at  the  station.  Both 
the  temperature  and  vapor  pressure  are  laid  off  positively  downward. 
The  sunshine  is  the  total  for  the  day  as  recorded  by  the  office  sunshine 
recorder. 

The  graph  as  a  whole  shows  a  rather  marked  similarity  in  the  nature 
of  the  several  curves.  In  many  cases  of  discrepancies  the  nucleation 
appears  to  show  the  effect  of  conflicting  causes.  On  November  29, 
with  no  sun,  the  nucleation  persists  from  the  fairly  high  reading  of 
the  day  before,  although  the  other  curves  drop.  Warm  rain  and 
further  increase  of  vapor  pressure  on  the  3oth  cut  it  down,  and  it 
ascends  very  slowly  during  the  cloudy  days  following.  A  decrease 
accompanies  the  rise  in  temperature  and  vapor  pressure  of  December 
5,  which  is  quickly  reversed  by  the  sunshine  and  northwest  wind  of 
the  6th.  The  nucleation  curve  remains  nearly  level,  as  doss  that  of 
the  water  vapor,  during  the  two  cloudy  days  succeeding.  The  sun- 


104      NUCLEATION   OF  THE  UNCONTAMINATED  ATMOSPHERE. 


shine  of  the  gth  and  nth  gives  maxima  which  themselves  rise  with 
the  moisture  and  temperature  curves,  while  all  drop  on  the  i2th.  The 
rise  on  December  13  seems  to  accompany  the  sudden  fall  in  tempera- 


I6&C.17     J8     19    <20    21    J22    30     3J 


JanZ  4  6     7  9     /O 


20 


10 


^    3     4     5    &    7     8 

FIG.  91. — Graphs  showing  current  nucleations,  etc.,  November  26  to  February  21. 


NUCLEATION   AT   BLOCK   ISLAND. 


105 


ture  and  change  of  wind  to  north.     The  maxima  of  the  i8th  lags 

behind  the  rest,  but  the  readings  fall  into  step  next  day. 

0  Increase  of  sunshine  on  January  i  shows'its  effect  on  the  nucleation, 


»IFt 

*k- 


3  24  25  26  27  28  29  30 
FIG.  92. — Graphs  showing  current  nucleations,  etc.,  February  21  to  May  3. 


106      NUCLEATION   OF  THE   UNCONTAMINATED   ATMOSPHERE. 


as  also  on  the  5th  and  i6th.  On  the  3d  the  nuclei  seem  to  have  been 
completely  wiped  out  by  rain,  and  we  get  no  more  till  the  sun  shines 
next  day.  From  the  i2th  to  the  [6th  the  nucleation  lags  behind  the 
other  curves  in  recuperating,  and  again  on  the  2ist  and  27th.  As 
is  often  the  case  for  low  values,  the  nucleation  does  not  follow  the 
other  curves  on  January  19.  During  the  last  days  of  the  month  the 
behavior  of  the  nuclei  is  quite  unusual,  although  the  snow  on  those 
days  is  light  and  dry. 

& 


Afi 


JMI.      Set.       eto/r.      cApr.     Mag. 


FIG.  93. — Chart  showing  the  average  daily  nucleations  at  Block  Island,  in  hundreds 
per  cubic  centimeter,  from  December  to  May,  1904-5. 


FIG.  94. — Location  of  the  stations  at  Providence  and  at  Block  Island. 


NUCLEATION   AT   BLOCK  ISLAND.  107 

The  dry,  cold  weather  of  February  gives  a  striking  series  of  maxima 
and  minima,  with  the  highest  readings  of  the  winter.  It  is  interesting 
to  note  the  fall  in  nucleation  on  the  5th,  accompanying  rise  in  tem- 
perature and  vapor  pressure,  and  east  wind,  although  the  sunshine 
remains  the  same.  Again,  on  the  i3th,  following  rain  in  the  night, 
the  vapor  pressure  and  nucleation  are  at  their  previous  value,  although 
there  is  no  sun  during  that  day.  On  the  2oth  the  nuclei  persist 
through  cloud  and  snow,  while  on  the  22d  they  disappear  entirely  with 
cloudy  weather. 

The  ist,  2d,  and  3d  of  March,  with  steady  sunshine  and  wind  con- 
stantly from  the  west,  show  well  the  agreement  between  the  nuclea- 
tion and  vapor  pressure.  On  the  6th,  one  notes  again  the  lag  of  the 
nucleation  in  building  up,  and  that  the  light  rain  and  fog  of  the  suc- 
ceeding days  does  not  cut  down  the  nucleation  entirely.  During  the 
rest  of  March  and  April  there  is  a  considerable  amount  of  water  vapor 
and  the  temperature  runs  higher  ;  the  uucleation,  while  it  follows  the 
changes  in  the  other  curves,  remains  low,  although  there  is  at  this 
period  plenty  of  sunshine.  The  rains  of  this  time  never  wash  out  the 
nuclei  entirely,  and  readings  of  several  thousand  are  often  obtained  in 
thick  fog. 

80.  Tentative  inferences. — Perhaps  the  most  striking  result  shown 
by  these  observations  is  the  variation  of  the  nucleation  with  change 
in  wind  direction.  It  is  very  probable  that  nuclei  are  brought  by  the 
land  breeze  from  towns  over  which  it  passes.  Our  winds  from  the 
northeast  to  southwest,  through  the  east,  are  pure  sea  breezes  ;  there 
is  no  land  in  those  directions  for  a  great  distance,  and  the  readings 
when  such  winds  occur  are  usually  low.  High  readings,  on  the  other 
hand,  commonly  accompany  wind  from  the  other  quadrants.  Such 
winds  (as  seen  in  fig.  94)  pass  over  towns  and  cities  comparatively 
near;  Newport,  R.  I.,  is  a  little  east  of  north  30  miles  distant;  the 
towns  on  the  Connecticut  shore  lie  between  northwest  and  west  at 
distances  from  20  miles  up  ;  New  York,  from  which  one  would  expect 
a  vast  number  of  nuclei,  is  a  little  south  of  west,  distant  about  100 
miles.  When  the  wind  is  from  this  quarter,  however,  the  nucleation 
is  as  a  rule  considerably  less  than  for  northwest  winds,  possibly  because 
the  nuclei  may  not  survive  so  long  a  journey. 

This  wind  effect,  however,  must  not  be  overestimated.  During  the 
winter  months  here,  clear,  cold  weather,  with  small  amountlof  water 
vapor,  occurs  quite  regularly  with  northwest  winds,  and  all  these  con- 
ditions usually  accompany  high  nucleation.  It  is  difficult  to  deter- 
mine the  active  factors  or  their  relative  influence  from  a  limited  series 


108      NUCLEATION   OF  THE  UNCONTAMINATED   ATMOSPHERE. 

of  observations  at  one  station,  particularly  as  the  prevailing  winds 
are  land  winds.  Data  from  places  where  the  northwest  wind  blows 
over  no  cities,  and  where  the  northwest  wind  is  warm  and  the  south- 
east wind  dry,  would  be  interesting. 

Again ,  the  daily  averages  of  the  nucleation  appear  to  vary  inversely 
with  those  of  the  temperature  and  vapor  pressure,  while  in  most  cases 
they  all  vary  directly  during  the  day,  rising  to  a  maximum  near  noon. 
This  would  seem  to  suggest  an  overbalancing  effect  of  the  sun  in  pro- 
ducing nuclei.  As  regards  the  relative  influence  of  temperature  and 
vapor  pressure,  one  might  look  for  an  increase  of  nucleation  after  a 
sudden  fall  of  temperature,  but  would  hardly  expect  nuclei  to  be  pro- 
duced because  of  continued  cold.  It  seems  quite  possible,  however, 
that,  with  a  high  vapor  pressure,  there  is  continual  condensation  of 
moisture  on  the  nuclei  present,  with  a  persistent  tendency  to  drag 
them  to  the  earth.  The  inverse  agreement  between  the  nucleation 
and  the  relative  humidity  is  even  more  general,  for  the  latter  more 
often  descends  to  a  minimum  during  the  day.  The  percentage  of 
saturation,  moreover,  ought  to  be  some  index  of  the  condensation 
taking  place,  remembering  that  condensation  may  be  in  progress  at 
higher  levels  when  the  air  at  the  surface  is  not  saturated,  and  that,  at 
those  planes,  small  variations  of  temperature  may  be  producing  satu- 
ration. The  absorption  of  the  sun's  rays,  if  they  produce  nuclei, 
would  also  have  some  effect,  but  probably  to  a  less  degree. 

In  the  case  of  sunshine  and  cloud,  likewise,  the  effect  is  obscured 
for  sudden  changes  by  variation  at  the  same  time  in  the  vapor  press- 
ure. The  cloud  effect  is  partly  the  opposite  of  that  attributable  to  the 
sun,  which  has  been  assumed  to  produce  nuclei  throughout  the  day 
in  the  upper  atmosphere.  Clouds  catch  these  if  they  come  within 
range,  and  prevent  the  formation  of  others  near  the  surface.  Clouds, 
however,  are  at  the  same  time  apt  to  be  an  index  of  a  region  denucle- 
ated  by  rain. 

The  persistence  of  nuclei  is  shown  in  two  ways.  Readings,  usually 
less  than  10,000,  are  often  obtained  through  several  days  of  cloud, 
snow,  fog,  and  even  light  rain.  These  have  either  penetrated  through 
the  clouds  or  they  have  been  brought  from  cities,  in  which  case  the 
land  effect  here  must  be  small.  Persistence,  and  therefore  the  sup- 
posed cumulative  action  of  the  sun,  is  shown  in  the  day  curve,  in  which 
the  3  o'clock  reading  is  nearly  as  high  as  that  at  noon,  although  the 
sun  is  then  as  low  as  at  9  o'clock.  Similarly,  the  lag  of  the  nuclea- 
tion in  building  up  after  rain,  or  after  a  persistent  cloud  effect,  would 
seem  to  indicate  the  cumulative  action  of  the  sun . 


NUCLEATION   AT   BLOCK   ISLAND. 


109 


Taken  as  a  whole,  therefore,  it  seems  to  me  probable  that  some- 
thing more  than  the  displacement  of  a  land  effect,  produced  artificially 
and  locally  elsewhere,  chiefly  by  combustion,  has  been  observed.  In 
other  words,  it  would  be  premature  to  attribute  the  phenomena  as  a 
whole  to  atmospheric  convection. 

TABLE  58. — Average  daily  nucleations  of  the  atmosphere  at  Block  Island,  1904-5. 


Date. 

^X.O-3. 

Date. 

£S£i. 

Date. 

jrxart 

Date. 

*X»rt 

1904. 

1905. 

1905. 

1905. 

Nov    21 

Tan        * 

8.1 

Feb.  14 

17  A. 

Mar.  26 

9T 

.iN  U  V  •     -61 

JdLl.          ^ 

1  /**r 

•  X 

22 

5 

— 

T  C 

50 

27 

37 

'  ' 

16 

*  j 
Q  c   e 

•y 
28 

*  / 

4c 

jj'  J 

*  j 

O  A 

g 

3c\ 

T7 

5Q 

2O 

I    3 

* 

•y 

3c 

1  1 

18 

*y 

17  Q 

30 

1.  1 

26 

7-9 

10 

•  J 

5-4 

19 

a.  /.y 
15-4 

3i 

6.2 

27 

9-5 

ii 

4.2 

20 

8.4 

Apr.     i 

8.8 

28 

8.6 

12 

2.1 

21 

5-5 

2 

3-0 

29 

7-3' 

13 

5-2 

22 

1.8 

3 

11.8 

30 

1.8 

14 

5-8 

23 

19.4 

4 

3-4 

Dec.     i 

2.6 

15 

6.2 

24 

16.7 

5 

2.8 

2 

3-3 

16 

15.0 

25 

13-3 

6 

4.4 

3 

3-7 

17 

8.3 

26 

7.8 

7 

16.2 

4 

5-6 

18 

5-6 

27 

19.7 

8 

7.0 

5 

19 

28 

14.0 

9 

6.6 

6 

e!i 

20 

6^3 

Mar.    i 

27.0 

10 

2-3 

7 

5-1 

21 

12.6 

2 

22.9 

ii 

1.8 

8 

4-7 

22 

3-4 

3 

18.9 

12 

4-4 

9 

8-3 

23 

12.7 

4 

8.7 

13 

1.4 

10 

2-5 

24 

2.1 

5 

8.5 

14 

5-7 

ii 

16.7 

25 

4.2 

6 

12.2 

15 

7.8 

12 

0.6 

26 

6.9 

7 

8.8 

16 

5-9 

13 

7-5 

27 

13-4 

8 

6.0 

17 

5.1 

14 

19.7 

28 

9-7 

9 

6.2 

18 

8.0 

15 

10.  1 

29 

5«o 

10 

7-7 

19 

5.4 

16 

5-5 

30 

8.2 

ii 

22.7 

20 

2.2 

17 

8.0 

31 

7-1 

12 

9.4 

21 

1.4 

18 

ii.  i 

Feb.     i 

13 

ii.  8 

22 

6.3 

19 

5-8 

2 

22.9 

14 

11.4 

23 

6.1 

20 

II-5 

3 

21.9 

15 

12.3 

24 

4-5 

21 

8.9 

4 

22.  0 

16 

7-9 

25 

5-6 

22 

IO.I 

5 

12.  0 

17 

7.8 

26 

4-3 

30 

8.4 

6 

1.2 

18 

5-9 

27 

2.2 

31 

3-7 

7 

23-4 

19 

5-7 

28 

1.4 

8 

I7.8 

20 

1.4 

29 

1.3 

1905. 

9 

I.O 

21 

I.O 

30 

4.2 

Jan.      i 

5.0 

10 

15-3 

22 

5-3 

May     i 

8.6 

2 

2.6 

ii 

21.9 

23 

2.8 

2 

2.1 

3 

o 

12 

6.1 

24 

1.6 

3 

4-5 

4 

4-9 

13 

6.6 

25 

4.0 

81.  Average  daily  nucleations  at  Block  Island.— The  mean  variations 
of  the  nucleation  at  Block  Island  from  day  to  day  are  given  in  table 
58,  and  they  have  been  already  charted  in  figures  91  and  92.  The 


110      NUCLEATION   OF  THE  UNCONTAMINATED   ATMOSPHERE. 

data  are  constructed  for  rapid  inspection  in  figure  102,  of  Chapter 
V  (lower  curve).  The  initial  (high)  observations  marked  with  a  circle 
were  made  with  the  same  apparatus  in  Providence.  The  curve  as  a 
whole  shows  two  well-defined  undulations,  one  extending  from 
December  into  the  beginning  of  January  and  the  other  from  this 
epoch  to  the  beginning  of  April.  After  this  the  data  are  scattering. 
Further  discussion  will  be  appropriately  given  in  connection  with  the 
corresponding  data  found  at  Providence  and  detailed  in  the  next 
chapter. 

82.  Average  monthly  nucleations  at  Block  Island.— Table  59,  below, 
contains  the  monthly  average  of  the  number  of  nuclei  in  the  atmos- 
phere of  Block  Island  in  thousands  per  cubic  centimeter.  The  data 
are  reproduced  in  figure  93.  The  curve  contains  definite  indica- 
tions of  a  maximum  in  December  practically  coinciding  with  those 
found  in  the  two  preceding  years  in  Providence,  as  suggested  by  the 
dotted  line.  After  January,  however,  the  enormous  increment  of 
nucleation  which  characterizes  the  February  observations  appears. 
This  is  the  feature  of  the  present  results,  and  the  effects  continue  with 
general  moderations  during  March  and  April ;  for  the  nucleation  of 
March  actually  exceeds  that  of  December,  while  April  is  not  much 
below  January,  showing,  therefore,  that  very  unusual  conditions  pre- 
vail in  the  atmosphere. 

To  interpret  this  curve,  /.  e.,  to  discriminate  between  terrestrial  and 
cosmical  interferences  with  the  atmosphere,  it  will  be  necessary  to 
compare  it  with  the  corresponding  monthly  distribution  of  the  meteoro- 
logical constants  of  the  atmosphere.  This  will  be  appropriately  done 
in  Chapter  V,  section  5,  in  connection  with  the  other  data  there  given. 

TABLE  59. — Average  monthly  nucleations  at  Block  Island,  1904-5. 

NX  iQ-3. 

*  November,  1904 <  7.0 

December,  1904 ....  7.  i 

January,  1905 5.4 

February,  1905 13.9 

March,  1905 7 .9 

April,  1905 5.0 

t  May,  1905 <  5.0 

*  November  21-30,  only.     Average  datum  therefore  too  high, 
t  May  1-3,  only.     Average  datum  therefore  much  too  high. 


CHAPTER  V. 

THE  COTEMPORANEOUS  NUCLEATIONS   OF  THE  ATMOSPHERE 
AT   PROVIDENCE   AND  AT   BLOCK  ISLAND. 

83.  Introductory.— In  the  preceding  chapter,  Mr.  R.  Pierce,  jr.,  has 
given  an  account  of  his  observations  of  the  nucleation  of  the  atmos- 
phere at  Block  Island.      I  purpose  in  this  place  to  give  the  corre- 
sponding data  for  Providence.     The  two  stations  lie  nearly  enough 
together  to  have  about  the  same  general  meteorological  elements, 
while  the  conditions  as  to  nucleation  may  be  totally  different.     Block 
Island  is  surrounded  by  a  body  of  water  the  least  radius  of  which, 
measured  from  the  center  of  the  island,  is  nearly  20  kilometers.     It 
lies  about  70  kilometers  from  Providence  in  a  direction  about  10°  west 
of  south.     Fully  one-half  of  Block  Island  fronts  the  ocean,  as  is  seen 
in  figure  94,  Chapter  IV.    The  atmosphere  at  the  former  place  should 
be  relatively  free  from  pollutions  due  to  the  habitation  of  man,  while 
the  reverse  is  naturally  true  of  the  latter.     It  is  unfortunate  that  in 
both  cases  the  prevailing  winds  are  land  winds,  at  least  from  a  distance, 
and  in  discussing  observations  it  must  be  borne  in  mind  that  the  wind 
bearing  is  not  indiscriminately  in  all  directions.     I  shall  at  the  same 
time  avail  myself  of  the  series  of  observations,  extending  over  two 
years,  contained  in  my  report*  to  the  Smithsonian  Institution,  which, 
with  the  present  series,  complete  a  three  years'  period. 

84.  Observations. — These  are  taken  with  less  frequency  than  in  the 
former  paper  (loc.  cit.),  but  are  otherwise  on  the  same  plan.     The 
entries  of  the  table  are  at  once  intelligible.     The  time  of  day  is  in  hours 
and  tenths  of  an  hour.     Weather  variations  are  noted  from  cloudy 
(C),  partly  cloudy  (FC)  to  fair  (F).     The  temperature  of  the  apparatus 
is  given  in  degrees  Centigrade;  those  of  the  atmosphere  in  degrees 
Fahrenheit.     The  coronal  diameter,  is  shown  under  s,  which  is  the 
chord  of  a  radius  of  30  cm.,  when  the  eye  at  the  goniometer  and  the 
source  of  light  are  85  cm.  and  250  cm.,  respectively,  from  the  fog 
chamber.     The  number  of  nuclei  per  cubic  centimeter,  given  under 
n,  has  not  been  corrected  for  temperature,  as  the  difference  for  the 
present  purposes  is  unessential. 

*  Smithsonian  Report,  vol.  xxxiv,  1905. 

in 


112      NUCLEATION  OF  THE  UNCONTAMINATED  ATMOSPHERE. 


TABLE  60. — Number  of  nuclei  (n)  per  cubic  centimeter  in  the  atmosphere  of  Provi- 
dence, R.  I.,  from  November  i,  1904,  to  May  i,  1905. 

[Weather:  C  cloudy,  CF  partly  cloudy,  F  fair.  Coronal  colors  (r  red,  b  blue,  p  purple, 
w  white,  o  orange,  y  yellow,  g  green,  br  brown)  are  given  from  the  center  outward.  An  accent 
denotes  an  approach  to  the  color  (y'  yellowish);  a  perpendicular  line,  a  thin  ring  of  indetermi- 
nable color.  If  0  is  the  angular  diameter  of  the  corona  measured  to  the  outside  of  the  first  red 
ring,  2  sin  0/2  =  */3O.] 


Date. 

Time 

Weather. 

Wind. 

Temp, 
of 
appa- 
ratus. 

Temp 
of 
atmos- 
phere. 

S. 

Corona 
colors. 

n. 
Num- 
ber. 

Remarks. 

1904. 
Nov.    1 

2 

Hour. 
9.6 
1.0 
4.0 
9.8 
4.2 
5  g 

F 
C 
C 
F 
F 
F 

W 
NW 

N 
N 
S 

°C 
16.1 
17.1 

17.1 
19.1 
19.1 

op 
50 
54 
53 
43 
48 
45 

cm. 
3.2 
3.1 
3.1 
3.1 
3.1 
6  4 

w    b    p 
w    b    p 
w    b    p 
w  o  g 
w|b|p 
w  r  g 

42,000 
38,000 
38,000 
38,000 
38,000 
86,000 

3 

4 

9.4 
11.9 

3.1 

10.4 
10.8 
11.3 
12  3 

C 
C 

C 

F 
F 
F 
F 

S 
S 

sw 

N 
....... 

18.1 
19.1 

19.1 

19.1 
20.1 
20.1 
20  1 

50 
53 

»{ 

55 

57 
57 

6.1 
5.1 
4-8 
4.8 
4.6 
5.1 
4.7 
3.9 

y'  eg 

w  |  b  |  p 

>  cor 

wrg 
w|b|p 

W  0  g 

cor 

75,000 
46,000 

39,000 

35,000 
46,000 
37,000 
21,000 

4.4 
6  0 

C 
C 

NW 

20.1 
20  1 

51 

47 

3.5 

3  8 

15,000 
19,000 

5 

10.  1 

1.0 
3.2 
6.1 

C 

C 
C 
C 

N 
N 
NE 

18.1 

19.1 
19.1 
21.1 

ti{ 

45 
42 
38 

3.5 
3.5 
4.6 

3.8 
4.9 

I   cor 

wrg 
wrg 
w|bjp 

15,000 

34,800 
19,000 
41,700 

6 

9.6 
11.8 
12  2 

C 
F 
F 

N 
NW 

18.1 
17.1 

37 
43 
44 

4.3 
5.4 
5.3 

cor 
wp  cor 

w|b|p 

28,000 
54,200 
50,500 

6.0 

F 

17.1 

42 

4.7 

wrg 

37,200 

7 

9.5 
12  0 

C 
F 

W 

15.1 
16  1 

*{ 

4.8 
4.8 
4.9 

g|b|p 
wrg 
g|b|p 

}  39,500 
41,700 

8 
9 

4.9 
10.5 
11-6 
9.5 
11  9 

F 
F 

F 
C 
Sn! 

'NW 

N  W 

17.1 
16.1 
17.1 
17.1 
17.1 

39 
42 
44 
37 
36 

4.8 
6.6 
5.8 
4.9 
6.3 

wrg 
w  o  bg 
w  eg' 
w!b|p 

y'rg 

39,500 
90,000 
64,500 
41,700 
80,500 

Repeated  same. 

10 

11 

12 

4.4 
6.0 
9.3 
11.7 

10.4 
5.5 
9.9 
9.9 
5  3 

C  Wet 
C 
F 
F 
F 
C 
F 
F 
F 
F 

N  W 

N 
S 

•"N"' 
w 
w 

18.1 
18.1 
17.1 
18.1 
19.1 
18.1 
20.1 
18-1 
18.1 
20  1 

37 
36 
37 
43 
43 
38 
34 
42 
47 
46 

5.5 

5.8 
6.6 
4.8 
5.5 
4.8 
6.2 
6.0 
6.0 
6  0 

wp  cor 
wrg 
y'org 
wrg 
wp  cor 

g'  I  b  1  P 
wrg 
wrpg 
wrpg 
w  rp  g 

56,200 
64,500 
90,000 
39,500 
56,200 
39,500 
76,500 
70,500 
70,500 
70,500 

Snow. 

13 

10.0 
12.6 
5  8 

R 
R 
R! 

w 

NK 

18.1 
18.1 
18.1 

46 
44 
42 

4.8 
3.8 
2.8 

w|b|p| 
cor 
cor 

39,500 
19,000 
7,300 

Gale! 

14 

9.4 
12.3 
4  2 

C 
C' 
C'  S 

NW 

NW 

17.1 
16.1 
17.1 

40 
43 
42 

5.0 
5.5 
7.0 

w|b|p 
wp  cor 
g'b'p' 

43,800 
56,200 
120,000 

Vapor. 

15 

16 

17 

4.8 
9.3 
12.7 
1.2 
3-0 
6-0 
9.4 
1.2 
5  0 

F 
F 
F 
F 
F 
F 
F 
F 

...^... 
NW 

"  NW'" 

•"N"' 

N 

17.1 
19.1 
20.1 
19.1 
20.1 
18.1 
19.1 
19.1 

41 
49 
50 
51 
44 
28 
32 
29 

6.1 

4.8 
5.3 
6.2 
4.8 
4.9 
6.3 
6.1 
4.8 

wrg 
g'bp 
wp  cor 
wrg 
wo  |  g 
g|b|p 
wrg 
wrg 
glbfp 

73,300 
39,500 
50,500 
76,500 
39,500 
41,700 
80,500 
73,300 
39,500 

18 

9.4 
12.4 
6  0 

F 
F 
F 

N 

17.1 
17.1 
20.1 

25 
32 
32 

5.7 
6.0 
6.3 

wrpg 
wrg 
w  ro  g 

61,500 
70,500 
80,500 

19 

9.3 
12.5 

F 
F 

NW 

19.1 

30 

5.8 
5.8 

wrpg 
}  wrpg 

64,500 
64,500 

NUCLEATION   AT   PROVIDENCE.  113 

TABLE  60. — Number  of  nuclei  («)  per  cubic  centimeter,  etc. — Continued. 


Date. 

Time. 

Weather. 

Wind. 

Temp, 
of 
appa- 
ratus. 

Temp, 
of 
atmos- 
>here. 

S. 

Corona 
colors. 

n. 
Num- 
ber. 

Remarks. 

1904. 
Nov.  19 

lour. 
3.3 
5  2 

F 
F 

NW 

°C 
20.1 
21.1 

°F 

52{ 

47 

cm. 
5.7 
5.0 
5.6 

wrpg 
wbr  cor 
w  p  g 

}  61  ,500 
58,700 

20 

9.8 
1.3 
5  6 

F 
F 

c 

No  wind 
W 

18.1 
18.1 
18.1 

46 

58 
52 

4.9 
4.6 
5.1 

g'lbfp 
wrg 
w  |  bjp 

41,700 
34,800 
46,000 

Haze. 

21 
22 

9.4 
12.3 
9.7 

F 
C' 
FH 

W 

NW 

18.1 
19.1 
19.1 

52 
51 
42 

4.5 

5.7 

wr  g 

wp  cor 

32,400 
61,500 

About  the  same. 

1.1 
6  0 

F 
F 

S 

20.1 
20.1 

46 
42 

5.0 
6.2 

wfb|p 
w  r  g 

43,800 
76,500 

23 
24 

9.0 
12.1 
5.8 
9.6 
12.0 
7.0 
9.6 

F 
F 
F 
C 
C 
F 
F 

NW 

"myj"' 

N 

19.1 
19.1 
19.1 
18.1 
18.1 
17.1 
19.1 

45 
52 
44 
42 
43 
41 
36 

4.8 
4.8 
4-8 
4.8 
5.3 
4.9 
4.6 

g'bp 
w  o  cor 
g'bp 
g'bp 
wp  cor 
w  |  br  |  p 
wo  g 

39,500 
39,500 
39,500 
39,500 
50,500 
41,700 
34,800 

Fog. 

25 

26 

9.8 
1.6 
4.7 
9.6 
12.2 

F 
C' 
C 
F 
F 

"NW"' 

NW 

16.1 
17.1 
17.1 
17.1 
18.1 

40 
42 
48 
33 
37 

6.7 
5.8 
4.6 
5.6 
5.6 

w  o  bg 
wp  cor 
wrg 
wrpg' 
w  rp  g' 

92,500 
64,500 
34,800 
58,700 
58,700 

5  e 

F 

19.1 

34 

5.7 

w  rp  g' 

61,500 

27 

9.0 
12  0 

F 
C 

N 

15.1 

25 
32 

5.6 
4.3 

wrp  |  g' 
wrg 

58,700 
28,000 

28 

9.7 
12.0 

F 
F 

NW 

14.1 
14.1 

24 

27 

6.3 
6.4 

wog 
w  y  g 

80,500 
83,500 

29 

5.0 
11.3 
11.9 
12  3 

F 
C 
C 

c 

"  '  s"  " 

SW 

15.1 
14.1 
14.1 
14  1 

26 
34 
38 

5.3 
7.0 
5.9 
5.9 

wp  cor 
w  o  bg 
wrpg 
w  rp  g 

50,500 
120,000 
68,000 
68,000 

Vapor. 

3.7 
5  g 

C 

c 

16.1 
16.1 

44 

48 

5-8 
6.2 

wrpg 
w  ro  g 

64,500 
76,500 

Rain  at  night. 

30 

9.3 
12.3 
6.0 

C 

c 
c 

W 
SW 

18.1 
19.1 
20.1 

53 
46 

6.2 

4-8 
5.4 

w  rog 
gbp 
wp  cor 

76,500 
39,500 
54,200 

Dec.    1 
2 

9.4 
3.5 
10.0 
1.5 
3.5 
6  0 

F 
C 
C' 
C 

c 
c 

W 

'  N  W 

NW 

N 

19.1 
19.1 
19.1 
19.1 
19.1 
19.1 

35 
37 
34 
36 
33 
28 

6.4 
5.8 
5.8 
5.8 
5.8 
5.8 

wog 
wrpg' 
wrpg' 
wrpg 
wrg 
wrg 

83.500 
64,500 
64,500 
64,500 
64,500 
64,500 

3 

9.3 
1.0 
3.2 
6  3 

c 
c 
c 
c 

N 
...^... 

18.1 
19.1 
19.1 
19  1 

23 
27 
27 
26 

5.8 
6.0 
6.0 
5.3 

wrg 
wog 
wog 
wp  cor 

64,500 
70,500 
70,500 
50,500 

Snow'. 

4 

9.5 
12.8 
4.3 
6  0 

F 
C 
C 
F 

NW 
W 
W 

17.1 
18.1 
19.1 
19.1 

25 
30 
29 

28 

5.3 
5.6 
5.6 

4.8 

wp  cor 
wpg' 
wpg' 
g'bp 

50,500 
58,700 
58,700 
39,500 

Repeated  same. 

5 

9.2 
10.6 
12.4 
3.3 
5  0 

F 
F 
C 
C 

c 

N 
S 

'"sw"" 

18.1 
18.1 
18.1 
18.1 
18.1 

26 

33 
32 

30 

6.8 
6.4 
4.9 
5.6 

4.8 

wgo 
wog 
gbp 
wrg 
w'  b  p 

95,000 
83,500 
41,700 
58,700 
39,500 

Snow  at  night. 

6 

9.3 
1  0 

F 
F 

NW 

18.1 
18.1 

30 
35 

5.8 
6.0 

wrpg 
w  rg 

64,500 
70,500 

7 

9.1 
1.6 
4.6 
6  0 

C 
F 
F 
F 

SW 

•  •  w  •  " 

18.1 
18.1 
19.1 
19.1 

23 
39 
37 
36 

6.5 
5.0 
6.0 
6.3 

wog 
w|bfp 
wrg 
wog 

86,500 
43,800 
70,500 
80,500 

8 
9 

9.5 
12.0 
4.1 
9.6 
12.0 
3.7 
6  0 

C 
C 
C 
F 
F 
F 
F 

s 

NE 
N 
W 
W 
W 

18.1 
18.1 
19.1 
17.1 
18.1 
17.1 
18.1 

29 
31 
31 
23 
25 
24 
20 

4.9 
4.8 
4.9 
6.8 
6.9 
6-8 
6.8 

g'  1  b  |  p 
wrg 
wog' 
w  o  bg 
wgo  bg 
w  ro  g 
w  ro  g 

41,700 
39,500 
41,700 
95,000 
100,000 
95,000 
95,000 

Snow'. 
Do. 

10 

9.5 
9  8 

C 

c 

N 

18.1 

15 

5.8 
6.6 

wrpg 
w  yo  g 

64,500 
90,000 

12.0 

C 

N 

18.1 

17 

6.8 

w'y  bg 

95,000 

114      NUCLEATION   OF  THE  UNCONTAMINATED  ATMOSPHERE. 


TABLE  60. — Number  of  nuclei  (n)  per  cubic  centimeter,  etc. — Continued. 


Date. 

Time. 

Weather. 

Wind. 

Temp, 
of 
appa- 
ratus. 

Temp, 
of 
atmos- 
phere. 

s. 

Corona 
colors. 

n. 
Num- 
ber. 

Remarks. 

1904. 
Dec.  10 
11 

Hour. 
4.0 
9.0 
12.7 
6.0 

C 
F 
F 
F 

N 
N 
NW 

18.1 
19.1 
21.1 
22.1 

°F 
16 
11 
19 
20 

cm. 

6.8 
6.8 
6.0 
6.1 

s'  y'  bg 

g'  y'  bg 

y'rg 

w  r  g 

95,000 
95,000 
70,500 
73,300 

Snow'. 

12 
13 

9.5 
12.0 
3.7 
9.0 
12.0 
4.0 

C' 
C 
Sn! 
Sn! 
C 
C 

N 
NE 
E 
N 
NE 

21.1 

20. 
22. 
22. 

21. 

19 
26 
26 
21 
25 
28 

7.1 
4.8 
4.9 
6.1 
5.9 
5.1 

wyg 
wrg 
w|bTp 
wrg 
wcg 
wbr  cor 

120,000 
39,500 
41,700 
73,300 
68,000 
46,000 

14 

9.2 
12.5 
3.5 

F 
F 
F 

NW 

22. 
21. 
20. 

13 
21 
23 

7.1 
7.0 

5.8 

gy  obg 
gy  o  bg 
wcg 

90,000 
90,000 
64,500 

5.6 

F 

21- 

20 

6.4 

w  o  g 

83,500 

15 

9.0 
12.4 

F 
C' 

N 

21. 
20. 

14 
26 

6.7 
7.0 

gbp 
w  oy  bg 

92,500 
100,000 

Repeated  same. 

3.0 
5.4 

C 
C 



21. 

28 
28 

6.7 
6.1 

wog 
wrg 

92,500 
73,300 

16 

9.0 
5  6 

C 
F 

N 

22. 
22 

30 
29 

6.7 
6.0 

gbp 
w  c  ar 

92,500 
70,500 

17 

8.7 
12.1 
3.4 
6.4 

F 
F 
C 
C 

NW 
...  „  ... 

18. 
20.1 
21.1 
21  1 

20 
30 
30 
30 

6.9 
6.2 
5.6 
6.3 

w  p  cor! 
wrg 
wp  cor 
wrg 

100,000 
76,500 
58,700 
80,500 

Snow!  at  night. 

18 

10.3 
12.3 
5  5 

C 
F 
F 

NW 
W 

23.1 
23.1 
23  1 

31 
32 

29 

4.8 
5.0 
5  5 

gbp 
w|b|r 
wp  cor 

39,500 
43,800 
56,200 

19 

9.7 
12  3 

C' 
C 

s 

23.1 
23  1 

27 
34 

6.3 

5  7 

wrg 
wp  cor 

80,500 
61,500 

5.1 

C 

23.1 

40 

6.4 

wrg 

83,500 

20 
21 

22 

9.2 
12.7 
3.7 
8.8 

12.7 

4.0 
5.8 

10-0 

12.7 
4.7 

F 
F 

C' 
C 

F 

C' 
F 

C 

C 
C 

NW 
W 

w 

W 

N 
NW 

W 

sw 

22.1 
23.1 
23.1 
23.1 

23.1 

23.1 
23.1 

22.1 

22.1 
22.1 

30 
35 

34 
31 

»{ 

28 
22 

*{ 

32 
31 

6-7 
6.0 
6.6 
6.0 
7.0 
6.7 
5.8 
5.2 
6.6 
6.8 
7.0 
6.2 

wyog' 
wcg 
wog 
wcg' 
wy'g' 
gbp 
wcg 
wp  cor 
gbp 
gbp 

gy  og' 

wrg 

92,500 
70,500 
90,000 
70,500 

[l20,000 

64,500 
48,200 

1  90,000 

90,000 
76,500 

6.0 

C 

31 

6  4 

wog 

83,500 

23 
24 

10.1 
1.0 
4.7 

6.0 
10.0 
12  7 

C 
C 
C 
C 
C 

c 

sw 
sw 

....... 

23.1 
23.1 
23.1 
23.1 
25.1 
24  1 

40 
47 
46 
46 
34 
29 

5.4 
5.5 
5.5 
5.5 
4.9 
4  0 

wpg' 
wp  cor 
wp  cor 
wpg 
w  o  cor 
w  br  cor 

54,200 
56,200 
56,200 
56,200 
41,700 
22,000 

4.7 

C 

24  1 

25 

4  5 

w  r  cor 

32,400 

6  0 

c 

4  5 

w  ro  g 

32,400 

25 
26 

10.4 
12.5 
5.2 
9.6 
12.0 
3-3 
6  3 

F 
F 
F 
C 
C 
C 

c 

N 
....... 

N 

23.1 
23.1 
23.1 
22.1 
22.1 
22.1 
22  1 

15 

21 
21 
25 

28 
29 

6.3 
5.8 
5.5 
6.2 
5.8 
5.6 
5  3 

w'rg 
wcg 
wp  cor 
wrg 
wcg' 
wp  |g' 
w  P  cor 

80,500 
64,500 
56,200 
76,500 
64,500 
58700 
50,500 

Do. 

27 

9.7 
12.6 
4.0 

6  7 

R 
R 
R' 
Fog 

SE 
S 

N 

23.1 
22.1 
22.1 
22  1 

38 
41 
42 
39 

4.8 
4.9 
6.1 
4  8 

woy  cor 
w|B|p 
wrg 
gbp 

39,500 
41,700 
73,300 
39,500 

Foggy. 
Do. 
Rain!  at  night. 

28 

10.0 
12.3 
3.5 

RL 
F' 
F' 

E 
W 

23.1 
23.1 
23.1 

39 
47 
42 

6.7 
5.3 
6  6 

w  o  bg 
w  P  cor 
w  ro  bg 

92,500 
50,500 
90,000 

Fog. 

31 

1905. 
Jan.     1 

6.0 
11.3 
12.5 
5.9 

9.3 
12.7 

F 
F 
C' 
F 

F 
F 

...  „  ... 
sw 

NW 
W 

23.1 
23.1 
23.1 
23.1 

25.1 
26.1 

34 
43 
46 
44 

46 
57 

5.8 
6.0 
6.1 
5.8 

5.0 
4.6 

wP|g 
wrg 
wrg 
wP|g 

w  o  cor 
w  r  cor 

64,500 
70,500 
73,300 
64,500 

43,800 
34,800 

Thaw. 

NUCLEATION   AT   PROVIDENCE.  115 

TABLE  60.  Number  of  nuclei  (n)  per  cubic  centimeter,  etc.  — Continued. 


Date. 

Time. 

Weather. 

Wind. 

Temp, 
of 
appa- 
ratus. 

Temp, 
of 
atmos- 
>here. 

S. 

Corona 
colors. 

n. 

Num- 
ber. 

Remarks. 

1905. 
Jan.  l 

Hour. 
5.6 

V 

°C 
25.1 

op 

44 

em. 
3  9 

cor 

20,500 

2 

9.5 
12.0 
5.7 

C' 

c 

CR' 

S 
S 

26.1 
26.1 
25.1 

41 
44 
44 

5.1 

5.8 
6.8 

w  br  b  |  r 
w  c  g 
wog 

46,000 
64,500 
95,000 

3 
4 
5 

9.4 

12.6 
3.5 
5.8 
9.8 
12.7 
3.3 
6.0 
10.0 
12.8 
6.0 

C  R' 
C 
CSn! 
C  Sn 
CSn! 
F 
F 
F 
F 
F 
F 

NK 
K 

....... 

N 

"  'w  "  ' 

w 

23.1 
23.1 
22.1 
22.1 
22.1 
21.1 
21.1 
21.1 
20.1 
20.1 
20.1 

37 
34 
30 
26 
17 
18 
17 
12 
14 
22 
18 

3.5 
4.0 
3.7 
4.7 
7.0 
6.9 
6.8 
6.0 
6.2 
6.6 
6.0 

cor 
cor 
cor 
w  b  p 
yobg 

yog 

y  org 
w  eg 
w  eg 

yog 

w  c  g 

15,000 
22,000 
17,500 
37,200 
120,000 
100,000 
95,000 
70,500 
76,500 
90,000 
70,500 

6 

9  5 

C  Sn 

20  1 

14 

6.8 

y'  O  g 

95,000 

12.7 

C 

20.1 

20 

6.0 

wcg 

70,500 

5  8 

C 

20.1 

30 

6.0 

w  c  g 

70,500 

Rain!  at  night. 

7 

9.5 

R! 

22.1 

49 

4.7 

W  0  |  g 

37,200 

Gale. 

8 

12-6 
9.7 
1.0 
6.0 

C 
F 
F 
F 

S 

w 
w 

22.1 
18.1 
17.1 
16.1 

48 
32 
34 
31 

5.6 
5.7 
6.0 
5.3 

w  P  cor 
w  P  cor 
wcg 
w  P  cor 

58,700 
61,500 
70,500 
50,500 

9 
10 

9.0 
11.8 
4.3 
10.0 
12.7 
6  0 

F 
F 
F 
F 
F' 
F 

w 

NW 

sw 
w 
w 

17.1 
17.1 
17.1 
20.1 
20.1 
20.1 

25 
31 
32 
37 
39 
29 

6.2 
5.0 
6.3 
5.7 
4.3 
4.9 

wcg 
w  P  cor 
wcg 
w  P  cor 
g'Bp 
w     B  |  p 

76,500 
43,800 
80,500 
61,500 
28,000 
41,700 

11 

9-1 

C 

21.1 

24 

4.7 

g'     B  1  p 

37,200 

4.3 

C 

20.1 

31 

4.7 

w'     B|p 

37,200 

6  0 

C 

21.1 

32 

4.6 

w'     B  |  p 

34,800 

12 
13 
14 

15 

9.5 
12.0 
3.5 
9.0 
4.0 
6.0 
10.1 
1.3 
4.3 
6.1 
10.7 
12.7 
6  0 

C  R' 
C 
R 
F 
C 
F' 
F 
F 
F 
F 
F 
F 
F 

S 

—jjrv 

NW 
N 

•••£•" 

NW 
W 

'  "w  "  ' 
w 

22.1 
22.1 
22.1 
23.1 
21.1 
21.1 
21.1 
19.1 
19.1 
20.1 
20.1 
20.1 
20.1 

35 
39 

40 
28 
28 
26 
19 
24 
20 
18 
18 
21 
22 

5.1 
6.6 
5.3 
5.3 
6.8 
5.8 
6.4 
6.7 
5.4 
5.5 
6.8 
6.6 
5.8 

w  P  cor 
w  o  g 
w  Br  cor 
w  Br  cor 
wog 
wc|g 
wcg 
wog 
w  Br  cor 
wP  |  g 
wog 
wog 
wPg 

46,000 
90,000 
50,500 
50,500 
95,000 
64,500 
83,500 
92,500 
54,200 
56,200 
95,000 
90,000 
64,500 

Fog. 

16 

9.4 
5.0 

F 
F 

w 

20.1 
19.1 

22 

28 

6.4 
6-9 

wog 
g  y  o  bg 

83,500 
100,000 

17 

9.7 
1.0 

F 
C 

w 

20.1 
19.1 

28 
35 

6.0 
6.0 

wcg 
wcg 

70,500 
70,500 

6  0 

21.1 

36 

6.2 

wr  g 

76.50U 

18 

9.4 
4.2 
6  0 

C' 
C 
C 

w 

N 

22.1 
21.1 
21.1 

33 
34 
34 

6.0 
4.4 
4.4 

wcg 
cor 
w  r  g 

70,500 
30,000 
30,000 

19 

20 

9-3 
12.3 
5.0 
9.7 
11.2 

F 
F 
F 
F 
F 

SW 

w 
w 
w 

22.1 
21.1 
21-1 
22.1 
22.1 

39 
46 
45 
41 
41 

5.3 
5.7 
6.0 
4.7 

4.8 

w  Br  cor 
w  P  cor 
wcg 
g    b[p 
g    b  |  p 

30,500 
61,500 
70,500 
37,200 
39,500 

6  3 

F 

22-1 

36 

5.5 

w  P  cor 

56,200 

21 
22 
23 
24 

9.7 
1.0 
6.1 
9.7 
1.0 
6.2 
9.3 
12.3 
5.0 
9.4 
1.2 
5  7 

F 
C' 
CSn 
C  R' 
C 
C 
F 
F 
F 
F 
F 
F 

NW 
...  „  ... 

W 

....... 

NW 
...„..., 

NW 

21.1 
22.1 
22.1 

23.1 
22.1 
20.1 
20.1 
21.1 
20.1 
20.1 

31 
37 
34 
49 
40 
38 
18 
22 
21 
14 
25 
26 

5.1 
5.1 
5.4 
5.7 
3.8 
4.7 
6.9 
5.7 
5.7 
5.7 
4.8 
4.7 

w  Br  cor 
w  Br  cor 
w  Br  cor 
wC 
cor 
wog 
gbp 
wcg 
wcg 
wcg 
w  or  g 
g'Bp 

46,000 
46,000 
54,200 
61,500 
19,000 
37,200 
100,000 
61,500 
61,500 
61,500 
39,500 
37,200 

- 

25 

10.3 

Sn 

20.1 

15 

5.9 

wcg 

68,000 

Gale  and  drift. 

Il6      NUCLEATION   OF  THE  UNCONTAMINATED  ATMOSPHERE. 


TABLE  60. — Number  of  nuclei  («)  per  cubic  centimeter,  etc. — Continued. 


Date. 

Time. 

Weather. 

Wind. 

Temp. 
of 
appa- 
ratus. 

Temp, 
of 
atmos- 
phere. 

s. 

Corona 
colors. 

n. 
Num- 
ber. 

Remarks. 

1905. 
Jan.  25 

Hour. 
12.4 

Sn 

°C 
20.1 

°F 
15 

cm. 
6.3 

w  r  g 

80,500 

Blizzard. 

5  7 

Sn 

19  1 

11 

7  0 

gy  o  bg 

90,000 

26 

9.5 
12.7 
6.0 

F 
F 
F 

NW 
N 

19.1 
18.1 
20.1 

10 
16 
16 

7.0 
6.6 
5.9 

gy  o  bg 
g(v)Bp 
w  c  g 

90,000 
100,000 
68,000 

27 

9.1 
12.2 
6  4 

F 
F 
F 

NW 
W 

20.1 
20.1 
21.1 

17 

27 
27 

7.1 
6.9 
6.5 

g'o  bg 
g'obg 
w  r  g 

90,000 
90,000 
86,500 

28 

9.7 
11.6 

Sn' 
C 

sw 

22.1 
22.1 

27 
32 

6.6 
6.5 

wcg 

w  r  g 

90,000 
86,500 

5  6 

c 

23  1 

24 

5.1 

w    B]  p 

46,000 

*  =  5.5  close  up. 

29 
30 

9.6 
12.7 
6.0 
9.3 
3  5 

F 
F 
F 
C 
C 

NW 

W 

22.1 
22.1 

22.1 
21  1 

19 
26 
25 
21 
24 

6.9 
4.8 
6.1 
5.8 
6.9 

w  or  g 
g'Bp 
wcg 
wPg' 
w  y  bg 

100,000 
39,500 
73,300 
64,500 
100,000 

s  =  7.7  close  up. 

s  =  7.3  close  up. 
s  =  6.8  close  up. 
=  7.7  close  up. 

5  0 

C 

21  1 

23 

6  4 

w  r  g 

83,500 

—  73  close  up. 

31 

9.5 
12  6 

F 
F 

N 

21.1 
21  1 

17 
23 

7.1 
7  0 

gy  o  bg 
w  o  g 

120,000 
120,000 

=  7.9  close  up. 
—  78  close  up. 

3  2 

F 

20.1 

23 

5.7 

w  P  cor 

61,500 

=  6.6  close  up. 

Feb.     l 

6.1 
9.5 
12.4 
6.0 

F 
F 
F 
F 

"NW"' 

21.1 
20.1 

20.1 

22 
17 
26 
27 

6.9 
6.1 
7.2 
6.2 

w  yo  g' 
wcg 
wy  g 
wcg 

100,000 
73,300 
120,000 
76,500 

=  7.9  close  up. 
=  7.4  close  up. 

=  7.4  close  up. 

2 
3 

9.4 
3.5 
9.4 
12  3 

F 
F 
F 
F 

w 
'  "w  •  " 

21.1 
20.1 
20.1 
20  1 

23 
22 

10 

17 

4.9 
5.8 
6.7 
6  8 

g'Bp 
wP  g' 

y'  o  bg 
y'  o  bg 

41,700 
64,500 
92,500 
95,000 

=  5.8  close  up. 
=  6.6  close  up. 

5  7 

F 

21  1 

16 

6  8 

w  o  bg 

95,000 

4 

9.8 
12.9 
4.0 
6.0 

F 
F 
F 
F 

NW 
W 
NW 

20.1 
19.1 

20.1 

10 
16 
18 
17 

7.0 
7.6 
5.8 
6.6 

gBP 
gy  obg 
w  P  cor 
gBP 

120,000 
120000 
64,500 
90,000 

5 

6 

9.8 
10.8 
12.9 
4.8 
9.3 
12.0 
5.0 
6.0 

F 
F 
F 
F 
Sn! 
R 
R 
R' 

N 

"w"' 

s 

NE 
E 

N 

19.1 

20.1 
20.1 
21.1 
21.1 
21.1 

15 

25 
25 
28 
32 
35 

6.7 
6.9 
6-7 
5.0 
4.8 
4.8 
6.6 

gBP 
gBP 
w  r  g 
w    B|P 
g'     B|P 
g'     B|P 
GBP 
g  y  o  bg 

92,500 
100,000 
92,500 
43,800 
39,500 
39,500 
90,000 
(90,000) 

7 
8 

9.2 
12.5 
4.3 
6.0 

9.6 
12  4 

F 
F 
F 
F 

F 
F 

W 

NW 
N 

N 

22.1 
21.1 
21.1 
21.1 

20.1 
20  1 

22 
23 
25 

22 

*{ 

30 

6.8 
6.0 
6.9 
5.9 
6.4t 
6.6J 
6  7 

w  o  g 
wCg 

y  o  bg 

wcg 
v'|B|RO 
gBP 

95,000 
70,500 
100,000 
68,000 

83,500 
92,500 

4.9 
6  0 

F 
F 

N 

21.1 

31 
31 

6.0 
6  8 

wcg 
gy  o  bg 

70,500 
95,000 

9 

10 

9.5 
12.5 

3.7 
5.0 
9.8 
12.1 
4.5 
6.0 

Sn! 
C 

R 
R' 
F 
C 
C' 
F 

N 
E 

E 

NE 
w 

NW 
NW 

22.1 
21.1 

20.1 
20.1 
23.1 
23.1 
21.1 
21.1 

26 
35 

35 
34 
37 
41 
34 
31 

5.5 

3.8 

4.3 
4.3 
5.1 
5.0 
4.4 
5.2 

w  P  cor 
cor 

wRlg 
wRJg 
w  P  cor 
S'  1  B  !  P 
wRgr 
w     B  1  p 

56,200 
19,000 

28,000 
28,000 
46,000 
43,800 
30,000 
48,200 

Small  corona  for  east 
wind. 

11 
12 
13 

9.3 
12.1 
5.1 
9.5 
12.5 
5.0 
9.4 
3.8 

F 
F 
F 
C 
C 
CSn 
R' 
R' 

W 
NW 
W 
W 
W 

w 
w 

22.1 
21.1 

20.1 
20.1 
21.1 
22.1 
20.1 

21 
25 
24 
20 
23 
29 
41 
29 

6.4 
6.5 
6.1 
6.7 
6.8 
5.6 
5.6 
4  8 

w  r  g 
wr  g 
wcg 
w  r  g 
wog 
w  P  cor 
w  P  cor 
wog 

83,500 
86,500 
73,300 
92,500 
95,000 
58,700 
58,700 
39500 

5  0 

25 

4  8 

wog 

39,500 

14 
15 

9.3 
12.4 
5.8 
9.5 

F 
F 
F 
F 

w 

w 
w 
w 

20.1 
20.1 

20.1 

10 
14 
17 
20 

6.8 
6.5 
6.8 
6.1 

yobg 
wog 
yobg 
wcg 

95,000 
86,500 
95,000 
73,300 

Haze. 

NUCLEATION  AT  PROVIDENCE.  117 

TABLE  60. — Number  of  nuclei  (w)  per  cubic  centimeter,  etc. — Continued. 


Date. 

Time. 

Weather. 

Wind. 

Temp, 
of 
appa- 
ratus. 

Temp, 
of 
atmos- 
phere. 

s. 

Corona 
colors. 

n. 

Num- 
ber. 

Remarks. 

1905- 
Feb.  15 
16 

Hour. 
5.6 
11.8 
3.5 
6  0 

F 
F 
F 
F 

NW 

NW 
NW 

20.1 
19.1 

20.1 
20  1 

op 

25 
16 
21 
19 

cm. 
5.2 
6.9 
6.0 

6  7 

w  1  Bi  P 
gBP 
wCg 
w  or  g 

48,200 
100,000 
70,500 
92  500 

17 

18 
19 

9.0 
12.3 
4.3 
6.5 
8.9 
12.5 
5.9 
10.3 

C 

c 

C 
C 
F 
F' 
F 
F 

sw 
sw 
sw 

'  •  'w  •  " 

NW 

NW 

20.1 
20.1 
20.1 
20.1 
22.1 
22.1 
21.1 
21.1 

28 
36 
35 
34 
21 
23 
18 
17 

6.9 
6.4 
6.4 
5.6 
6.6 
6.4 
6.0 
6.7 

w  o  g 
wrg 
wrg 
w  P  cor 
w  o  g 
wog 
wrg 
wog 

100,000 
83,500 
83,500 
58.700 
90,000 
83,500 
70,500 
92,500 

12.7 

4.8 

F 
F 

W 

21.1 
21.1 

21 
24 

7.0 
5.0 

w  o  bg 
g'BP 

120,000 
43,800 

6  4 

F 

21  1 

23 

6  2 

w  R  g 

76,500 

20 

7.9 

C 

21.1 

34 

6.2 

w  C  g 

76,500 

12  3 

Sn! 

20.1 

33 

5.6 

w  P  cor 

58,700 

21 
22 

23 
24 

6.0 
9.7 
12.2 
9.5 
12.3 
5.8 
9.4 
12-0 
5.1 
9.7 
12.3 

R' 
F 
F 
C 
C 
C 
F 
F 
F 
C 
C 

...^... 

N 

NF, 
NE) 

"NF,"" 
'  'NFJ 

N 

21.1 
23.1 
23.1 
23.1 
23.1 
23.1 
22.1 
22.1 
23.1 
22.1 

36 
41 
45 
32 
33 
31 
21 
26 
33 
33 
38 

5.7 
6.2 
6.0 
4.3 
4.8 
4.3 
7.1 
6.9 
5.2 
6.8 

wrg 
w  c  |  g 
w  P  cor 
cor 
cor 
g'  o  bg 

yog 

w  Br  cor 
gBP 

61,500 
76,500 
70,500 
28,000 
39,500 
28,000 
90,000 
100,000 
48,200 
95,000 

26 

4.0 
9  7 

F 

C' 

NW 

23.1 
23  1 

41 
36 

5.7 

6.7 

wP|g 
wog 

61,500 
92,500 

27 

28 

12.4 
5.5 
9.4 
4.3 
9.3 
12.7 
3.9 
6  1 

c 
c 

F 
F 
F 
C 
F 
F 

s 

W 

w 
w 
w 
w 
w 

23.1 
23.1 
23.1 
20.1 
23.1 
21.1 
21.1 
22  1 

40 
40 
24 
30 
30 
38 
39 
38 

5.0 
4.4 

6.8 
5.8 
4.9 
6.4 

4.8 
4  7 

w  br  cor 
w  r  cor 
wog 
w  P  cor 
g'BP 
wog 
g'Bp 
g   B  p 

43,800 
30,000 
95,000 
64,500 
41,700 
83,500 
39,500 
37,200 

Mar.    1 

10.1 
12.4 
6  2 

F 
F 

F 

w 
w 

21.1 
20.1 
21.1 

29 
32 
30 

6.0 
6.0 
5.4 

w  C  g 

WCg 

cor 

70,500 
70,500 
54,200 

2 

9.3 
3.5 
5  0 

F 
F 
F 

NW 
W 

20.1 
20.1 
20.1 

22 
32 
31 

6.5 
5.1 
5.4 

wog 
w  Br  cor 
w  P  cor 

86,500 
46,000 
54,200 

3 

9.7 
12.2 
6  3 

F 
F 

F 

w 
w 

21.1 
20.1 
22  1 

30 
35 
36 

6.8 
6.3 
5.6 

wog 
wrg 
w  P  cor 

95,000 
80,500 
58,700 

4 
5 

9.2 
12.0 
5.8 
9.7 
1.1 
7-0 

C' 
C 
F 
F 
F 
F 

s 
w 

N 
N 
S 

23.1 
22.1 
22.1 
21.1 
21.1 
21.1 

37 
43 
35 
23 
29 
28 

5.9 
4.7 
5.3 
6.2 
5.5 
5.0 

wrg 
wrg 
cor 
wog 
w  P  cor 
w  Br  cor 

68,000 
37,200 
50,500 
76,500 
56,200 
43,800 

6 

7 

9.2 
4.3 
6.7 
9.7 
1.0 
6  1 

F 
F 
F 
F 
C' 
C 

NW 
N 

"  "s  "  ' 

S 

22.1 
20.1 
20.1 
21.1 
21.1 
21.1 

29 
35 
33 
31 
38 
35 

6.8 
4-8 
5.9 
5-2 
4.7 
4.7 

wog 
cor 
wrg 
w  br  cor 
w|BjP 
w  j  B  |  P 

95,000 
39,500 
68,000 
48,200 
37,200 
37,200 

8 
9 

10 
11 

9.5 
3.2 
5.3 
9.5 
1.4 
5.0 
9.2 
5.1 
9.3 
1  0 

C 
C 
C 
F 
C' 
C 

c 
c 

F 
F 

N 
W 
SW 
NW 
S 
S 
N 
S 
W 

21.1 
21.1 
21.1 
23.1 
23.1 

23.1 
23.1 
23.1 
23.1 

39 
42 
40 
40 
45 
40 
40 
47 
31 
35 

5.7 
6.4 
4.7 
4.7 
4.6 
4.6 
4.9 
4.9 
7.0 
6.1 

wrg 
wrg 
wBP 
wBP 
wrg 
wog 
wog 
wog 
wobg 
wrg 

61,500 
83,500 
37,200 
37,200 
34,800 
34,800 
41,700 
41,700 
90,000 
73,300 

Fog. 
Fog. 

Rain!  at  night. 

12 

6.0 
9.8 
4.6 

F 
F 
C' 

W 

w 

23.1 
23.1 
23.1 

32 
36 
41 

4.8 
5.6 
5.0 

wBP 
w  P  cor 
g'BP 

39,500 
58,700 
43,800 

Il8      NUCLEATION  OF  THE  UNCONTAMINATED  ATMOSPHERE. 

TABLE  60. — Number  of  nuclei  (w)  per  cubic  centimeter,  etc. — Continued. 


Date. 

Time. 

Weather. 

Wind. 

Temp, 
of 
appa- 
ratus. 

Temp, 
of 
atmos- 
phere. 

*. 

Corona 
colors. 

n. 
Num- 
ber. 

Remarks. 

1905. 
Mar.  13 

14 

Hour. 
9.5 
12.3 
6.3 
9.3 
12.5 
6  3 

F 
F 
F 
F 
F 
F 

N 
W 

s 

N 
N 

°C 
22.1 
22.1 
22.1 
20.1 
21.1 
21  1 

op 

29 
34 
31 
31 
38 
32 

cm. 
5.5 
5.9 
6.2 
5.3 
4.9 
4  8 

w  P  cor 
wrg 
wcg 
cor 
wo  cor 
wo  cor 

56,200 
68,000 
76,500 
50,500 
41,700 
39,500 

15 
16 

9-7 
12.0 
5.8 
9.7 
1  0 

F 
F 
F 
F 
F 

NE 
N 
S 
NW 

22.1 
22.1 
22.1 
22.1 
22  1 

31 
37 
35 
43 

49 

6.0 
5.6 
5.0 
5.7 
4  8 

wcg 
w  P  cor 

w  P  cor 
g'  B  P 

70,500 
58,700 
43,800 
61,500 
39,500 

6  0 

F 

23.1 

44 

4.6 

cor 

34,800 

17 

9.5 
2.6 
6  2 

F 
F 
F 

NE 

23.1 
23.1 
23.1 

39 
46 
39 

5.0 
4.7 
4.5 

w|B|P 
g'BP 
wrg 

43,800 
37,200 
32,400 

18 

9.6 
1.5 

6  5 

F 
F 
F 

s 

S 

23.1 
23.1 
23.1 

46 
63 
52 

4.8 
4.8 
4.6 

gBP 
gBP 
wrg 

39,500 
39,500 
34,800 

19 
20 

9.6 
9-7 
6.0 

R' 
R' 
C 

W 

NE 

22.1 
20.1 
20.1 

53 
36 
34 

4.5 
3.8 
4.8 

w  o  g 
cor 
wB  P 

32,400 
19,000 
39,500 

21 

9.4 
3.3 

C  R' 
RSn 

NE 

20.1 
20.1 

36 
34 

3.5 
3.6 

cor 
cor 

15,000 
16,200 

22 
23 

6.0 
9.5 
12.6 
6.0 
9.4 
1.0 
6.2 

R' 
C 

C' 
F 
F 
F 
F 

........ 

N 
NE 
SE 
S 

20.1 
21.1 
21.1 
22.1 
19.1 

21.1 

32 
35 
41 
37 
39 
44 
38 

3.7 
5.2 

4.8 
4.8 
4.8 
4.8 
5.5 

cor 
w  P  cor 
wy  g 
wyg 
gBP 
gBP 
wcg 

17,500 
48,200 
39,500 
39,500 
39,500 
39,500 
56,200 

24 

9-3 
1.3 

C 
C 

S 

22.1 
22.1 

40 
43 

5.4 

4.8 

w  P  cor 
wrg 

54,200 
39,500 

25 

9.5 
1.3 

R 
C 

S 

23.1 
23.1 

48 
53 

4.7 

4.8 

wrg 
w  o  g 

37,200 
39,500 

26 

27 

28 
29 
30 

10.0 
1.5 
6.8 
9.5 
3.0 
5-5 
9.1 
6.4 
8.7 
6.4 
10.3 
12-7 
6-2 

F 
F 
F 
C 
C 
F 
F 
F 
F 
F 
C' 
F 
F 

W 
W 

s 
sw 

W 

W 
W 
W 

NE 
S 

s 
s 

24.1 
24.1 
24.1 
25.1 
24.1 
24.1 
24.1 
24.1 
23.1 
22.1 
21.1 
21.1 
21.1 

52 

60 
48 
54 
58 
55 
56 
62 
57 
53 
52 
54 

4.8 
5.3 
4.6 
4.9 
4.9 
4.7 
4.7 
5.6 
4.6 
4.6 
4.0 
3.7 
4.6 

wBP 
w  P  cor 
wrg 

W  0  g 
W  0  g 

W  BP 
gBp 
wcg 
wrg 
wrg 
cor 
cor 

39,500 
50,500 
34,800 
41,700 
41,700 
37,200 
37,200 
58,700 
34,800 
34,800 
22,000 
17,500 
34,800 

31 
Apr.    1 

2 

9.2 
12.3 
9-5 
4-2 
6.4 
9-5 
1.5 
6.7 

F 
F 
F 
F 
F 
F 
F 
F 

W 

NW 
NW 
W 

N 
NW 
NW 

19.1 
19.1 
19.1 
19.1 
19.1 
17.1 
17.1 
17.1 

57 
64 
50 
50 
45 
37 
45 
41 

5.6 
5.2 
6.2 
4.9 

4.8 
5.3 
6.5 

5.8 

w  P  cor 
w|B|P 

W  0  g 

w|BTP 
w  P  cor 
w  P  cor 
w  o  g 
w  Cr  g 

58,700 
48,200 
76,500 
41,700 
39,500 
50,500 
86,500 
64,500 

3 
4 
5 

9.3 
3-4 
6-0 
9-4 
2.7 
6-3 
9-1 
3  3 

F 
F 
F 
R' 
C 
C 
C 
R 

W 

NW 
W 

NE 
s 

S 

N 

16.1 
17.1 
17.1 
17.1 
18.1 
19.1 
20.1 
20.1 

44 
57 
54 
45 
49 
47 
46 
47 

6.6 
6.1 
4.8 
4.7 
4.9 
4.6 
6.0 
3.8 

gBP8 
wcg 
w|  B|- 
gBP 
wo  g 

wcg 
cor 

90,000 
73,300 
39,500 
37,200 
41,700 
34,800 
70,500 
19,000 

6 

5.5 
9-0 
12.8 
6.4 

R 
R 

C 
F 

NE 
S 
SW 

21.1 
22.1 
22.1 

46 
49 
52 
47 

3.8 
4.6 
4.6 
4.7 

cor 
w  o  g 
wog 
gBP 

19,000 
34,800 
34,800 
37,200 

Fog. 

7 

9.3 
3.0 
6  1 

F 
F 
F 

N 
NW 

20.1 
19.1 

44 
51 
47 

4.8 
4.7 
4.8 

IBP 

wBP 
wrg 

39,500 
37,200 
39,500 

8 

9.0 
1.5 

C 
F 

W 

18.1 
18.1 

41 
50 

5.0 
5.0 

w|B|P 
cor 

43,800 
43,800 

NUCLEATION   AT   PROVIDENCE.  119 

TABLE  60. — Number  of  nuclei  (n)  per  cubic  centimeter,  etc. — Continued. 


Date. 

Time. 

Weather. 

I 

Wind. 

Temp, 
of 
appa- 
ratus. 

Temp, 
of 
atmos. 
phere. 

s. 

Corona 
colors. 

n. 
Num- 
ber. 

Remarks. 

1905. 
Apr.  8 
9 

10 

Hour. 
6.0 
9.7 
12.1 
5.6 
9.0 
12.5 

F 
F 
F 
F 
F 
F 

NW 
W 
W 
W 
SW 

18.1 
20.1 
21.1 
21.1 

20.1 

°  jr 
43 
48 
56 
56 
56 
65 

cm. 
4.4 
6.2 
4.7 
4.6 
5.5 
4.9 

cor 
w  o  g 
wrg 
wrg 
w  P  cor 
cor 

30,000 
76,500 
37,200 
34,800 
56,200 
41,700 

6.5 

F 

4.7 

cor 

37,200 

11 
12 
13 

9.3 
12.3 
5.7 
9.6 
3.4 
6.2 
9.4 
12.7 
6.5 

R! 
R 
R' 
C 
F 
F 
C 
C 
C 

NF, 
N 
NF, 
N 

N 

s 

NF, 

23.1 
22.1 
23.1 
19.1 
22.1 
22.1 
21.1 
21.1 

49 
49 
45 
49 
58 
52 
51 
55 

3.5 
3.6 
3.4 
4.8 
4.9 
4.8 
4.1 
4.3 
3.6 

cor 
cor 
cor 
cor 
w|  B|P 
w  rg 
cor 
cor 
cor 

15,000 
16,200 
13,800 
39,500 
41,700 
39,500 
24,000 
28,000 
16,200 

14 
15 
16 

9.4 
12.4 
6.3 
9.5 
1.5 
6.2 
10.3 
1.1 
6.5 

F 
F 
F 
F 
F 
F 
C' 
C 
C 

W 

...  „  ... 

N 
W 
NW 
NW 
W 

20.1 
20.1 
20.1 
18.1 
19.1 
20.1 
19.1 
19.1 
20.1 

50 
58 
52 
48 
54 
51 
49 
52 
42 

6.1 

5.8 
4.6 
6.4 
4.8 
4.7 
4.8 
3.8 
3.8 

wcg 
wp  cor 
wrg 
wrg 
wrg 
wrg 
w|B|P 
cor 
cor 

73,300 
64,500 
34,800 
83,500 
39,500 
37,200 
39,500 
19,000 
19,000 

17 

18 

9.7 
12.4 
6.3 
10  4 

C' 
C 
F 

C' 

W 

17.1 

17.1 
19  1 

41 
48 
42 
48 

5.6 
6.2 
5.1 

5.0 

wp  cor 
wp  cor 
w  f  B    P 
w    B    P 

58,700 
76,500 
46,000 
43,800 

1.0 

C 

20.1 

49 

4.9 

G|  B    P 

41,700 

6.0 

C' 

20  1 

43 

4.7 

wrg 

37,200 

24 
25 

3.8 
6.3 
9.7 
12.8 

F 

F 
F 
F 

s 

SW 

NW 

20.1 
19.1 
18.1 
19  1 

58 
53 
52 
60 

5.9 
4.9 
4.9 
4.9 

wcg 
gBP 
w  o  cor 
w  o  cor 

68,000 
41,700 
41,700 
41,700 

26 

6.0 
9.0 
4.5 

F 
C' 

R' 

W 

SW 

19. 
20. 
21 

62 
62 
69 

4.8 
5.4 
4.8 

cor 
w  P  cor 
gBP 

39,500 
54,200 
39,500 

27 
28 

9.6 
6.1 
9.5 
12.4 

C 

C' 
C 
C' 

NF, 

'"NE"' 

21. 
20. 
20. 
20. 

57 
58 
51 
57 

3.5 
3.5 
3.2 
3.0 

cor 
cor 
cor 
cor 

15,000 
15,000 
11,300 
9,300 

29 

6.2 
9.5 
12.5 
3.7 

F 
C 
C' 

E 

S 

20. 
18. 
19. 
20. 

59 

50 
60 

3.5 
3.3 
5.2 

4.0 

cor 
cor 
w  B  cor 

15,000 
12,500 
48,200 
22,000 

30 
May    1 

10.0 
12.7 
6.6 
9.4 
6.5 

F 
F 
C' 
F 
F 

w 
s 

NW 
NW 

19. 
19. 

20. 
18. 
18. 

65 
67 
64 
52 

4.4 
4.4 
3.7 
4.8 
4.0 

cor 
cor 
cor 
wocor 
cor 

30,000 
30,000 
17,500 
39,500 
22,000 

2 
3 

9.7 
4.0 
9.5 
3  8 

F 
F 
C' 
F 

NW 
W 
W 

18. 
19. 
19. 
21. 

51 
62 
66 
74 

5.5 
5.6 
5.6 
5.5 

wcg 
wp  cor 
w  P  cor 
w  P  cor 

56,200 
58,700 
58,700 
56,200 

6.0 

F 

SW 

21. 

70 

4.9 

wBP 

41,700 

All  data  are  given  in  the  upper  curves  of  figures  95  to  101,  the 
abscissas  showing  the  current  times,  the  ordinates  the  nucleations, 
in  thousands  per  cubic  centimeter.  The  usual  symbols  of  wind  and 
weather  are  inserted,  R  denoting  rain,  R'  rainish,  Sn  snow,  etc.  The 
lower  curves  have  already  been  referred  to  and  are  the  cotemporane- 
ous  data  found  by  Mr.  Pierce  at  Block  Island. 


120      NUCLEATION  OF  THE  UNCONTAMINATED  ATMOSPHERE. 

85.  Comparison  of  the  data  for  Providence  and  for  Block  Island. — A 

discussion  of  the  details  of  the  type  of  results  obtained  for  Providence 
has  already  been  given  in  the  Smithsonian  report  (loc.  cit.),  and  the 
new  data  add  no  essential  novelty.  It  will  suffice,  therefore,  to  com- 
pare the  two  classes  of  curves  throughout  their  extent. 

Figures  95  to  101  show  the  daily  record  of  the  nucleations  of  Provi- 
dence (upper  curve)  and  of  Block  Island  (lower  curve)  in  thousands 


,-u; 

^ 

X 

\ 

IV 

r 

f 

»>w 

\ 

i 

\ 

i 

t 

K 

/<'- 

> 

3.X, 

x  •*• 

\  /on 

-0-0 

\ 
\ 
\ 

40 
on 

$ 

$ 

i 

i 

-•#0 

; 

5 

A** 

1 

f 

», 

r 

54-' 

4H 

53 

57° 

45* 

44° 

36* 

4 

4* 

36* 

/ 

^3 

38' 

47° 

44-'  X 

43 

1 

fa    ; 

^ 

' 

I           4 

I- 

5         ( 

J           7 

I 

i 

)           /( 

) 

/ 

/           / 

f 

/c 

A 

A 

80 

C(\ 

K 

A 

r 

1 

/    > 

/I 

l\ 

p. 

fcU 

1 

\ 

\ 
\ 

I 

1 

/ 

V 

Si 

i 

' 

y 

\ 
\ 
\ 

/\ 

|  x 

/  ^ 
37* 

>/ 

\ 
27 

1 

40 

49' 

** 

a 

I 

32' 

32*. 

52.' 

V 

-0 

58' 

V 

A 

6* 

52° 

j 

*.v 

o     ^* 
42° 

4'.- 

38' 

--i 

J 

i 
'. 

/ 

SJ-ar.    1 

s 

/ 

7          1 

3        /; 

}          2 

0        2 

/         2 

3 

3         2 

4 

' 

5        2 

6         2 

7         2 

8 

2 

FIG.  95.— Showing  daily  record  for  November  i  to  29. 

of  nuclei  per  cubic  centimeter  for  the  dates  given  by  the  abscissas, 
z".  e.,  from  November,  1904,  to  May,  1905.  The  prevailing  winds  and 
weather  and  the  temperatures  of  both  places  are  roughly  given  on  the 
curves. 

In  the  earlier  results,  from  November,  1904,  to  January,  1905,  there 
is  as  yet  no  striking  opportunity  for  comparison,  except  that  both 
cases  show  a  general  rise  of  nucleation  to  the  high  maximum  follow- 
ing December  14  and  December  20.  It  is  clear  that  similarity  in  the 


NUCI.EATION   AT   PROVIDENCE   AND   BLOCK   ISLAND.  12 1 

two  cases  must  be  marred  by  the  snow  effect,  which  is  necessarily  of 
unequal  value  in  the  two  cases,  the  depression  being  as  a  rule  larger 
and  more  striking  as  the  antecedent  nucleation  is  higher.  On  Decem- 
ber 12  the  two  curves  behave  similarly,  but  not  so  December  3,  8,  13, 
18,  21.  The  remarkable  depression  of  the  upper  curve  on  December 


I38sc.  14 


IS       16        17        18        19        30        21        22       23        24       US 

FIG.  96.  —  Showing  daily  record  for  November  29  to  December  27. 


24  is  noteworthy.  Some  instances  of  detailed  similarity  (December  4, 
9,  20,  etc.)  might  be  pointed  out,  but  in  general  the  curves  in  their 
details  are  dissimilar. 

Differences  in  winds  and  temperatures,  here  as  elsewhere,  are  in  the 
main  influenced  by  the  times  at  which  observations  were  severally 
made.  The  two  sets  of  results  show,  as  a  whole  (beginning  with 
November  27),  the  state  of  high  contamination  of  the  atmosphere  of 
Providence  as  compared  with  that  of  Block  Island.  Rarely  do  the 


122      NUCLEATION    OF  THE   UNCONTAMINATED  ATMOSPHERE. 

former  curves  dip  down  to  meet  the  latter,  while  the  nucleation  may 
be  50  or  more  times  greater.  The  difference  must  be  due  (since  it  is 
exaggerated  in  the  winter  months)  to  the  originally  ionized  products 
of  combustion.  The  two  curves  give  evidence  of  a  rapid  self-purifica- 
tion (probably  due  to  dilution)  of  the  atmosphere,  from  which  it  follows 
that  the  nuclei  observed  in  Providence  are  to  a  large  extent  generated 


lOjfen    11          1Z         /3          14          15         16          11          IS         /9          20         2J         22        23        24 
FIG.  97.— Showing  daily  record  for  December  27  to  January  24. 

there.  It  would  be  hazardous  to  assume,  however,  that  all  the  nuclei 
are  artificially  generated,  and  Mr.  Pierce  is  of  the  opinion  that  there 
is  an  outstanding  nucleation  in  the  Block  Island  results  which  can 
not  in  this  manner  be  explained  away. 

The  early  part  of  January  is  subject  to  rains,  and  the  sustained 
maximum  at  Providence  following  January  4  is  but  obscurely  repre- 
sented at  Block  Island.  On  the  other  hand,  the  maximum  following 


NUCIvEATlON   AT   PROVIDENCE   AND   BLOCK   ISLAND.  133 

January  13  is  fairly  well  reproduced  at  Block  Island  and  coincident 
high  values  on  January  16  are  probably  not  due  to  chance.  The 
same  may  be  said  of  January  23. 

Toward  the  end  of  February  the  pronounced  maximum  in  the  Block 
Island  results  (February  23-26)  is  in  keeping  with  the  Providence 
data.  The  sustained  high  wave  of  nucleation  at  Block  Island  from 


9          10          11          /2         13          14         IS         16         17         18 
FIG.  98.— Showing  daily  record  for  January  24  to  February  21. 

February  26  to  March  4  does  not  correspond  to  an  equally  sustained 
case  at  Providence,  though  the  nucleation  is  at  times  high.  In  this 
region  there  are  instances  (not  cotemporaneous,  however)  in  which 
the  Block  Island  nucleation  exceeds  that  of  Providence. 

Following  January  25  the  extremely  high  nucleations  which  hold 
general  sway  up  to  February  6  are  well  reproduced  by  both  curves. 
There  are  here  some  striking  coincidences,  as  on  February  i,  8,  etc., 


124      NUCLEATION   OF  THE  UNCONTAMINATED  ATMOSPHERE. 

with  divergences  on  February  2,  3,  etc.  The  exceptionally  high 
results  for  Block  Island  on  February  n,  14,  16,  18,  penetrate,  as  it 
were,  into  corresponding  elevations  in  the  upper  curve.  In  fact, 
between  February  10  and  20  the  wave  of  both  places  is  of  the  same 
general  type,  with  the  Providence  data  somewhat  behind  the  other  in 
phase.  This  is  one  of  the  most  interesting  parts  of  the  results.  It 
may  be  seen  more  or  less  clearly  on  February  3,  4,  7,  n,  14,  16,  18. 


Mar   8 


/O        //         tt        /3         /4         /5        /€         II        18 

FIG.  99.—  Showing  daily  record  for  February  21  to  March  21. 


Late  in  March  (8-20)  there  is  a  final  attempt  at  a  sustained  maxi- 
mum at  Block  Island,  while  the  Providence  data  gradually  decrease 
to  the  rain  on  March  20.  From  March  20  to  March  31  both  curves 
are  relatively  low.  March  31  to  April  4,  April  6  to  April  n,  April 
14  to  April  1  8,  show  a  distinct  tendency  of  both  curves  to  pass  through 
moderate  maxima.  The  remaining  data  to  March  4  are  too  low  for 
further  comparison.  As  a  whole,  therefore,  little  more  than  a  general 
correspondence  can  be  made  out,  in  which  the  correspondence  of  excep- 
tionally high  winter  nucleation  correspond  in  the  data  of  both  stations. 


NUCIvEATlON   AT   PROVIDENCE  AND   BLOCK  ISLAND.  125 


50' 

•H 

57* 

A 

":'j 

4 

""      |\  1 

'  V~1 

34* 

41° 

A 

7 

~'\3 

53* 

60" 

58* 

/ 

i 
\ 

54* 

/y 

A, 

X* 

\ 

i 

/w 

»  - 

'"1 

4- 

#*-o 

~*o« 

/ 

46* 

J-1* 

ffrSn 

JT 

•'< 

36° 

38* 

42' 

Vv 

1    4^ 

^ 

4C-* 

n* 

*A 

43* 
o 

-'     • 

J 

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,-A: 

\\Mar.  i 

^      2 

3         2 

4         2 

5        2 

6         2 

7         2 

8        2 

9         3 

a  45°3 

/             / 

^3r 

^ 

3          4 

6  7          8  9          /'J          //    4j"  /i          /3          /J          15 

FIG.  loo.—  Showing  daily  record  for  March  21  to  April  18. 


17 


9 

r-f\ 

^ 

"1 

bO 

4^ 
20 

A 
60 

44 
2.0 

/ 

49° 
•  V 

i>*^- 

.-"^ 

58 
it 

60* 

/ 
—  »«w  / 

69* 

A 

58' 

5t'- 

..  60' 

i 

67* 

52" 

*f 

0 

tj  o» 

J*    \ 

fv 

i.Ii 

I 

^ 

A 

429 

A- 

42* 

--A-. 

46* 

--! 

40' 

S^ 
^  - 

46* 
-e» 

49' 

-A. 

47* 

or 

52* 
Ji*~ 

r^lJ 

5/e 

>*     - 
—  X. 

?    foj49- 
r-^~ 

^ 

JJL 

-*4 

42!t 
-^ 

• 

.-€ 

^A 

.^ 

34*    &         2Q        21         ZZ       23        24        Z5        2£        27        28        M        W         way  .* 

^' 
G2' 

^ 

7^1 

45* 

o 

«i 

53* 
0 
--**«-. 

bEJ  3         4 

FIG.  loi.— -Showing  daily  record  for  April  18  to  May  4. 


126      NUCLEATION   OF  THE  UNCONTAMINATED  ATMOSPHERE. 


TABLE  61. — Average  daily  nucleations  of  the  atmosphere  at  Providence,  1904-5. 


Date. 

Weather. 

NX  10-3. 

Date. 

Weather. 

^X10-3. 

Date. 

Weather. 

-ZVX10-3. 

1904. 

1905. 

1905. 

Nov.    i 

FC 

39 

Jan.    i 

F 

33 

Mar.  2 

F 

62 

2 

F 

54 

2 

CR' 

68 

3 

F 

78 

3 

C 

53 

3 

CRSn 

23 

4 

CF 

52 

4 

F 

29 

4 

C  Sn  F 

96 

5 

F 

59 

5 

C 

27 

5 

F 

79 

6 

F 

67 

6 

CF 

42 

6 

C  Sn 

79 

7 

FC 

4i 

7 

CF 

40 

7 

R 

48 

8 

C 

61 

8 

F 

77 

8 

F 

61 

9 

FC 

36 

9 

Sn 

61 

9 

F 

67 

10 

C 

42 

10 

F 

62 

10 

F 

43 

ii 

F 

61 

ii 

CF 

58 

ii 

C 

36 

12 

FC 

5i 

12 

F 

7i 

12 

CR 

62 

13 

F 

67 

13 

R 

22 

13 

FC 

70 

H 

F 

44 

14 

CF 

73 

14 

F 

95 

15 

F 

58 

15 

F 

55 

J5 

F 

83 

16 

F 

44 

16 

F 

41 

16 

F 

92 

17 

F 

38 

17 

F 

64 

J7 

FC 

72 

18 

F 

38 

18 

F 

7i 

18 

C 

43 

19 

R' 

32 

19 

F 

62 

19 

F 

61 

20 

R'C 

29 

20 

F 

4i 

20 

F 

44 

21 

RSn 

16 

21 

F 

32 

21 

FC  Sn 

49 

22 

C 

42 

22 

F 

60 

22 

C 

39 

23 

F 

45 

23 

F 

39 

23 

F 

78 

24 

C 

47 

24 

CF 

42 

24 

F 

46 

25 

RC 

38 

25 

FC 

62 

25 

Sn 

80 

26 

F 

41 

26 

F 

59 

26 

F 

86 

27 

CF 

40 

27 

FC 

43 

27 

F 

89 

28 

F 

48 

28 

F 

7i 

28 

Sn'C 

74 

29 

F 

35 

29 

C 

80 

29 

F 

71 

30 

F 

25 

30 

C 

57 

30 

C 

83 

31 

F 

53 

Dec.     i 

FC 

74 

31 

F 

100 

Apr.  i 

F 

52 

2 

C 

64 

Feb.  i 

F 

90 

2 

F 

67 

3 

C 

64 

2 

F 

53 

3 

F 

67 

4 

FC 

52 

3 

F 

93 

4 

R'C 

38 

5 

FC 

63 

4 

F 

98 

5 

R 

36 

6 

F 

67 

5 

F 

82 

6 

RF 

36 

7 

CF 

70 

6 

Sn'R 

65 

7 

F 

39 

8 

C 

4i 

7 

F 

84 

8 

CF 

39 

9 

F 

96 

8 

F 

85 

9 

F 

49 

10 

C 

86 

9 

SnR 

33 

10 

F 

45 

ii 

F 

80 

10 

FC 

42 

ii 

R 

15 

12 

Sn 

67 

ii 

F 

81 

12 

CF 

40 

13 

Sn 

62 

12 

CSn 

82 

13 

C 

23 

14 

F 

82 

13 

R 

44 

14 

F 

57 

15 

FC 

90 

14 

F 

92 

15 

F 

53 

16 

CF 

81 

15 

F 

61 

16 

C 

26 

17 

FC  Sn 

79 

16 

F 

88 

17 

CF 

60 

18 

CF 

43 

17 

C 

81 

18 

C 

41 

19 

C 

75 

18 

F 

81 

.... 

20 

F 

84 

19 

F 

83 

24 

F 

55 

21 

CF 

76 

20 

Sn  R 

65 

25 

F 

41 

22 

C 

85 

21 

F 

73 

26 

CR' 

47 

23 

C 

56 

22 

C 

32 

27 

f 

15 

24 

C 

32 

23 

F 

79 

28 

CF 

12 

25 

F 

67 

24 

CF 

78 

29 

C 

28 

26 

C 

62 

25 

.... 

30 

FC 

26 

27 

R 

48 

26 

C 

55 

May  i 

F 

31 

28 

RF 

74 

27 

F 

80 

2 

F 

57 

.... 

28 

F 

51 

3 

F 

52 

31 

F 

69 

Mar.  i 

F 

65 

NUCLEATION    AT   PROVIDENCE   AND   BLOCK   ISLAND. 


127 


86.  Average  daily  nucleations.— These  are  given  in  table  61 ,  together 
with  the  date  and  the  weather.  They  are  further  shown  in  the  chart, 
figure  102,  where  the  abscissas  denote  the  successive  days  and  the 
ordinates  are  the  corresponding  nucleations  in  thousands  per  cubic 
centimeter.  The  different  points  are  distinguished  by  the  usual 
Weather  Bureau  symbols,  •  (|  ©  ,  r,  Sn,  etc.,  so  that  the  weather 
conditions  are  included  in  the  curves. 


201— 


40 


20 


J>otf'l904 


FIG.  102,  —  Average  daily  nucleations  in  thousands  per  cubic  centimeter  at  Providence 
(upper  curve)  and  at  Block  Island  (lower  curve,  excepting  the  data  marked 
with  a  circle,  which  were  taken  at  Providence)  for  November,  1904,  to  May, 
1905. 

This  curve  is  quite  distinct  from  the  types  obtained  in  1902-3  and 
1903-4  and  shown  in  my  earlier  report,*  inasmuch  as  the  new  curve 
has  an  incidental  strongly  marked  maximum  in  February.  Other 
features,  however,  appear  as  in  the  earlier  figures.  Thus,  there  is  a 
definite  tendency  to  reach  a  maximum  in  December. 


*  Smithsonian  Contributions,  Vol.  XXXIV,  1905. 


128      NUCLEATION   OF  THE  UNCONTAMINATED  ATMOSPHERE. 
TABLE  62. — Average  monthly  nucleations. 


TVTnnt-Vi 

Providence. 

Block  Island. 

Ratio. 

n  X  10-3. 

n'  X  10-3. 

n\n'. 

November. 
December. 
January  .  .  . 
^February.  . 
March  .... 
April       .  .  . 

53-0 
68.6 
66.1 

7i-5 
47.0 
/to  ^ 

<(7-o) 
7-i 
5-4 
13-9 
7-9 
50 

9-7 
12.3 

5-i 
5-9 

8.1 

May  

<(5-i) 

*The  February  effect,    which  is  merely  superimposed  at  Providence,   becomes 
fundamental  at  Block  Island.     The  ratios  show  that  it  outlasts  March  and  even  April. 


Oct.   M.  $&>.  Jew.  $d-  Aar.  Jpr  Jhy  Jum,  July 


Oct.  Jlfcv. 


FIG.  103. — Average  monthly  nucleations  at  Providence  in  thousands  per  cubic  centi- 
meter from  October,  1902,  to  May,  1905.  The  lower  curve  shows  corre- 
sponding results  taken  at  Block  Island. 

87.  Average  monthly  nucleations.— The  properties  of  the  new  curve 
just  referred  to  appear  more  obviously  if  the  monthly  averages  are 
drawn  in  their  dependence  on  time,  as  is  done  in  table  62  and  in 
figure  103.  In  the  latter  the  data  for  1902-3  and  1903-4  are  included, 
the  points  of  the  different  curves  being  suitably  distinguished.  The 
tendency  to  reach  a  maximum  in  December  appears  in  all  these  curves, 
but  the  curve  for  1904-5  departs  from  them  in  its  pronounced  march 
toward  the  duplicate  maximum  in  February,  after  which,  however, 
there  is  clear  agreement  between  the  1903-4  and  1904-5  curves,  neither 
of  which  falls  to  the  low  nucleations  for  March,  April,  etc.,  in  1902-3. 


NUCLEATION   AT   PROVIDENCE   AND   BLOCK   ISLAND. 


129 


The  chart,  moreover,  contains  the  average  monthly  nucleations 
observed  by  Mr.  Pierce  at  Block  Island.  It  is  interesting  to  note  that 
the  general  march  here  is  the  same  as  at  Providence,  a  definite  tendency 
toward  a  maximum  in  December  and  then  a  relatively  enormous  maxi- 
mum in  February,  from  which  there  is  slow  descent  to  the  summer 
nucleation  which  would  be  nearly  vanishing.  To  accentuate  these 
relations,  figure  104  has  been  drawn,  in  which  the  nucleations  at 
Providence  and  at  Block  Island  are  given  in  ten  thousands  and  in 
thousands  of  nuclei  per  cubic  centimeter,  respectively.  The  same 
February  disturbance  is  thus  superimposed  on  the  high  local  nuclea- 
tions due  to  combustion,  etc.,  at  Providence,  which  exists  in  compara- 
tive freedom  from  local  discrepancy  at  Block  Island.  It  is  hard  to 
resist  the  conclusion  that  so  marked  an  interference  with  the  usual 
distribution  of  nucleation  can  result  from  local  or  terrestrial  causes. 
Thus,  the  average  March  nucleation  at  Block  Island  exceeds  the 
December  nucleation,  while  the  April  nucleation  is  nearly  as  high  as 
the  January  nucleation. 

(4 


FIG.  104.— Average  monthly  nucleations  from  November,  1904,  to  May,  1905,  at  Provi- 
dence in  ten  thousands  per  cubic  centimeter,  and  at  Block  Island  in  thousands 
per  cubic  centimeter,  showing  the  probable  run  of  the  curves  in  the  absence 
of  the  February  maximum  and  the  coincidence  of  the  maximaland  the  minima. 


130      NUCLEATION  OF  THE  UNCONTAMINATED  ATMOSPHERE. 


Mr.  Pierce  has  compiled  the  following  summary  of  monthly  averages 
of  vapor  pressure,  temperature,  barometer,  sunshine,  rainfall,  etc. 
Of  these  the  data  for  temperature  and  precipitation  are  most  important. 
The  latter  was,  in  fact,  a  minimum  (0.05)  in  February,  but  differing  in 
value  but  slightly  from  November  (0.06)  and  March  (0.07).  It  is  not 
probable  that  any  effect  was  thus  produced.  Similarly  the  tempera- 
ture is  a  minimum  in  February  (25°),  differing,  however,  by  but  3° 
from  January  (28°),  while  the  nucleation  is  more  than  doubled 
(14/5.4).  Moreover,  the  December  maximum  of  nucleation  does  not 
exist  for  temperature.  It  seems,  therefore,  equally  improbable  that 
for  so  small  a  difference  of  temperature,  so  enormous  differences  in 
general  combustion  (if  this  were  the  cause)  could  be  evoked ,  and  more 
likely  that  both  the  temperature  minimum  and  the  nucleation  are 
different  effects  of  some  other  common  cause. 

TABLE  63. — Meteorological  Data. 


Average  values  of  — 

1904. 

1905. 

Nov.  26-30. 

Dec.  1-22, 
30,  31- 

January. 

Febru- 
ary. 

March. 

159 

38 
68 

3-3 
.06 
13-0 
22.3 
.00 

I.O 

.46 

128 
30 
76 
2.7 
.09 
11.4 
22.9 

•23 

.78 
.70 

116 
28 
73 
6.4 
.08 
11.7 
24.2 
.19 
.81 
•44 

96 

25 
70 
6.8 
•05 

12.  1 
22.2 

.18 
.82 
.40 

1  66 
32 
81 

7.8 
.07 
10.8 
15-5 
•37 
•63 
•47 

Range  of  temperature  variation  .  . 
^Vind.  velocity  (hours) 

NE   to  S          

SW   to  N       

Cloudiness  

There  does  not,  therefore,  seem  to  be  in  the  weather  conditions  in 
February  any  reason  for  so  marked  a  change  in  the  nucleation. 
Neither  is  the  temperature  low  enough  nor  the  rains  sufficiently  infre- 
quent to  account  for  the  accumulation  of  nucleation  observed. 

These  facts  also  appear  in  the  ratios  in  table  62,  showing  that  whereas 
the  Providence  nucleation  was  10  to  12  times  larger  in  December  and 
January  than  the  Block  Island  nucleations,  the  ratios  fall  off  to  but  5 
in  February,  from  which  low  datum  they  slowly  recuperate. 

88.  Conclusion. — While  the  Block  Island  observations  have  there- 
fore proved  that  much  the  greater  part  of  the  nucleations  observed  at 
Providence  is  of  local  origin,  it  has  not  proved  that  all  of  it  is  of  this 
character.  In  fact,  there  remains  a  residue  of  5  to  10  per  cent  of  the 


NUCLEATION   AT   PROVIDENCE   AND   BLOCK   ISLAND.  131 

observed  nucleation  in  question ,  which  is  still  present  and  undergoing 
phenomenal  variations  in  places  remote  from  the  habitations  of  man. 

Moreover,  the  arithmetical  character  of  the  fluctuation  of  nucleation 
in  the  lapse  of  time  is  the  same  at  the  two  stations,  however  widely 
the  geometrical  character  may  differ.  It  is  thus  probable  that  in  both 
cases  there  is  superimposed  on  a  local  nucleation  (large  at  Providence 
and  vanishing  at  Block  Island),  fairly  constant  for  long  periods  during 
the  winter  months,  a  specific  effect,  due  to  causes  which  are  certainly 
not  local.  In  fact,  the  same  character  of  variations  was  observed  at 
the  two  stations  in  spite  of  the  fact  that  the  air  under  examination  is 
necessarily  quite  different. 

The  outstanding  February  maximum  may  be  a  distant  land  effect, 
due  to  artificial  causes,  chiefly  combustion,  and  nearly  uniformly  dis- 
tributed over  the  whole  inhabited  territory ;  but  from  the  suddenness 
of  its  appearance,  its  pronounced  character,  and  the  extended  occur- 
rence as  instanced  at  both  stations,  one  is  tempted  to  regard  it  as  an 
actual  invasion  of  the  atmosphere  on  the  part  of  some  external  radia- 
tion or  nuclei-producing  agency. 

It  would  have  been  better  if  the  pressure  difference  at  the  station, 
where  the  air  is  relatively  pure  had  been  more  nearly  equal  to  the  fog 
limit  of  dust-free  air  (  8^=22),  i.  e.,  decidedly  above  the  fog  limit  for 
ionized  air  (8/>  — 19);  but  at  the  outset  it  was  thought  wise  to  avoid 
this  complication.  In  such  a  case  the  coronas  reached  by  the  present 
method  (8^  =  17)  would  all  have  been  obtained;  but  in  the  compara- 
tive absence  of  ordinary  nuclei,  a  response  from  ionized  material  might 
be  anticipated.  The  treatment  of  filtered  air,  however,  for  purposes 
like  the  present  or  the  interpretation  of  the  results  obtained  is  an 
extremely  precarious  matter,  as  I  shall  point  out  in  a  subsequent 
paper.  Meanwhile  we  may  note  that  the  curve  of  average  monthly 
nucleations  is  apt  to  show  a  maximum  and  minimum,  respectively,  at 
about  the  time  of  the  winter  and  summer  solstices,  and  that  any  defi- 
nite fluctuation  from  this  curve  is  due  to  causes  which  are  at  least 
nonlocal  in  character. 


CHAPTER  VI. 

SUMMARY  AND  CONCLUSIONS. 

89.  Introductory. — Researches  have  been  made  both  with  respect  to 
the  ordinary  relatively  large  or  dust-like  nuclei  contained,  i.  e.,  such 
as  will  not  pass  through  the  cotton  filter,  and  with  respect  to  the 
nuclei  much  smaller  in  size  and  probably  belonging  to  the  molecular 
system  of  air,  as  they  are  inseparable  from  it  by  nitration.  Nuclei  of 
the  former  class  are  usually  (though  not  necessarily)  foreign  in  char- 
acter. Those  of  the  latter  class  may  also  be  so ;  but  as  they  are 
demonstrably  small,  even  when  compared  with  the  ions,  and  are 
speedily  reestablished  if  withdrawn  from  the  air,  their  true  nature  may 
be  that  of  colloidal  air  molecules.  Being  present  in  thousands  and 
millions  per  cubic  centimeter,  in  proportion  as  the  order  of  molecular 
size  is  approached,  they  are  not  to  be  identified  with  the  ions  for  this 
reason  alone,  as  the  number  of  the  latter  is  insignificant  in  compari- 
son. From  what  has  been  stated,  colloidal  air  molecules  (nuclei)  can 
not  be  regarded  as  stable  chemical  bodies,  since,  if  precipitated  by 
condensation,  they  are  immediately  reproduced  in  the  medium  of  moist 
air  out  of  which  the  precipitation  took  place.  They  can  not  be  brought 
to  vanish  in  long  periods  of  decay.  In  fact,  the  coronas  of  filtered  air 
attain  their  maximum  size  after  long  waiting;  for  in  this  way  all  other 
larger  nuclei  which  may  incidentally  be  present  are  brought  to  vanish. 

Hence  one  must  conclude  that  the  nuclei  which  pass  the  filter  are 
present  in  a  definite  ratio  dependent  on  the  conditions  of  chemical 
equilibrium  of  the  most  general  kind.*  As  a  rule,  for  each  such 
nucleus  which  decays,  another  is  generated  in  the  nonenergized  dust- 
free  air  in  question,  leaving  the  nuclear  status  constant. 

If  we,  furthermore,  suppose  that  the  formation  of  a  nucleus  is  accom- 
panied by  the  expulsion  or  the  absorption  of  a  corpuscle  representing 
the  ionization ,  it  is  clear  that  a  very  high  degree  of  nucleation  may 
be  compatible  with  a  very  low  order  of  ionization,  such  as  is  the  case 
with  ordinary  dust-free  air  ;  for  the  concomitant  ionization  represents 
the  degree  to  which  a  decaying  nucleus  is  not  at  once  replaced  by  a 
newly  generated  nucleus  of  the  same  type,  and  vice  versa.  In  other 
words,  the  ionization  present  represents  the  oscillation  of  the  system 

*  Including  the  effect  of  internal  and  possibly  external  radiations. 
132 


FLEETING  NUCLEI.  133 

around  its  state  of  chemical  equilibrium,  the  sense  of  the  departure 
being  in  the  long  run  as  frequently  positive  as  negative. 

These  are  the  chief  features  of  the  hypothesis  by  which  I  have  been 
guided  in  my  work.  It  will  now  be  desirable  to  present  an  outline 
of  such  facts  bearing  on  the  whole  question  as  occur  in  my  own 
researches.  To  obtain  sufficiently  varied  conditions  it  will  manifestly 
be  necessary  to  produce  nuclei  in  the  condensation  chamber  (briefly 
called  the  fog  chamber)  itself,  without  introducing  foreign  material. 
This  may  be  done  by  aid  of  the  X-rays  or  the  beta  and  gamma  rays  of 
radium,  preferably  to  the  exclusion  of  the  emanation  and  even  of  the 
alpha  rays.  Changes  of  nucleation  so  obtained  may  be  regarded  as 
arising  out  of  the  dust-free  contents  of  the  fog  chamber. 

90.  Notation. — The  nucleations,  N,  referred  to  in  these  paragraphs, 
are  computed  from  the  angular  radius,  <£,  of  the  corona  seen  in  the 
fog  chamber  and  the  quantity  of  water  precipitated  in  the  given  exhaus- 
tion, in  the  way  detailed  in  my  report  to  the  Smithsonian  Institution 
(1905).     In  the  figures,  which  for  brevity  are  referred  to  in  place  of  the 
tables,  D  denotes  the  distance  of  the  X-ray  bulb  or  the  radium  tube 
(of  thin  aluminum,  hermetically  sealed)  from  the  near  end  of  the  fog 
chamber.     Exp.  is  the  time  of  exposure  in  minutes  to  the  radiation 
stated;  Lp,  the  lapse  of  time  after  exposure  to  the  radiation  ceases, 
or  the  time  during  which  the  nuclei  under  observation  are  left  without 
interference.       The  abscissas  (unless  otherwise  specified)  frequently 
indicate  the  number  of  an  observation  ;  i.e.,  they  are  merely  distribu- 
tive and  represent  the  character  of  successive  phenomena  to  the  eye. 
The  fog  chambers  used  were  sometimes  rectangular  boxes  of  wood 
impregnated  with  wax  and  provided  with  plate-glass  windows ;  at 
other  times  clear  glass  cylinders,  15  cm.  long  and  15  cm.  or  more  in 
diameter.     The  latter  case  insures  greater  freedom  from  traces  of 
leakage,  but  coronal  aperture,  2  <j>,  must  be  measured  parallel  to  the 
axis  of  the  cylinder.     Usually  the  chord,  s,  for  a  radius  of  30  cm. 
will  be  given,  so  that  2  sin  <(>  =  5/30. 

Exhaustions  are  preferably  made  at  a  pressure  difference  (8^) 
between  the  outside  and  inside  of  the  fog  chamber,  just  below  the  point 
(to  be  called  fog  limit  8/>0)  at  which  dust-free  nonenergized  saturated 
air  condenses  without  foreign  nuclei.  S^0  depends  on  the  particular 
apparatus  used, 

91.  Fleeting  nuclei — Ions. — Let  the  X-radiation  to  which  the  dust- 
free  air  is  exposed  be  relatively  weak,  so  that  the  density  of  ionization 
may  remain  below  a  certain  critical  value.     The  nuclei  observed  on 
condensation   are   then  very  small,  and  they  require  a  high  order 


134      NUCLEATION  OF  THE  UNCONTAMINATKD  ATMOSPHERE. 

of  exhaustion,  approaching  but  always  below  the  fog  limit  of  non- 
energized  air.  They  are  usually  instantaneously  generated  (within  a 
second)  by  the  radiation,  so  that  their  number  is  definite  independent  of 
the  time  of  exposure.  They  decay  in  a  few  seconds  after  the  radiation 
ceases,  i.  e.  ,  roughly,  to  one-half  their  number  in  2  seconds  to  one-fifth 
in  20  seconds,  in  the  usual  way.  (Cf.  Chapter  III,  figs.  42,  43.)  I 
fancy  that  these  nuclei  are  what  most  physicists  would  call  ions  ;  but 
nevertheless  the  particles  are  not  of  a  size,  the  dimensions  depending 
on  the  intensity  of  the  penetrating  radiation  to  which  they  are  usually 
due,  and  they  pass  continuously  into  the  persistent  nuclei,  as  shown  in 
the  next  paragraph,  where  decay  of  ionization  and  of  nucleation  are 
very  different  things.  They  are  abundantly  produced  by  the  y-rays, 
which,  though  weak  ionizers,  become  from  this  point  of  view  strong 
nucleators  (section  16).  Finally  (section  6)  they  are  stable  on  solution. 
The  case  seems  rather  to  be  one  in  which  the  rate  of  decay  exceeds 
the  rate  of  production.  The  following  is  an  example  of  data  bearing 
on  this  case,  N  being  the  number  of  nuclei  caught  per  cubic  centimeter 
of  the  dust-free  air  at  normal  pressure.  The  anticathode  is  at  a  dis- 
tance from  the  fog  chamber  and  the  exhaustion  carried  to  the  verge 
of  the  fog  limit  of  dust-free  air. 

Time  of  exposure  (rays  on)  ........  o  5  15  30  60  120  sees. 

^X  lo"3,  ......................  *i.6  74  74  •   •  74 

Time  after  exposure  (rays  off),  .  .  .  o  5  15  30  60  120  sees. 

.......................  92  30  23  18  10  4 


The  two  series  refer  respectively  to  generation  and  to  decay.  f 
If  N  is  expressed  in  thousands  of  nuclei  per  cubic  centimeter,  and 
time,  /,  reckoned  in  seconds,  and  if  ilN=a-\-bt,  so  the  dN\dt—  —  bNz, 
the  datum  £=0.002  reproduces  the  results  satisfactorily,  while  a  simple 
exponential  law  will  not  do  so.  The  decay  is  of  the  kind  characteriz- 
ing mutual  action  between  ions.  In  figures  42,  44,  Chapter  III,  com- 
puted data  are  distinguished  by  crosses. 

92.  Fog  limits  Of  fleeting  nuclei.  —  The  mean  increment  of  nucleation, 
8  TV,  per  centimeter  of  increment  of  pressure  difference,  8/>,  varies 
very  rapidly  as  compared  with  the  fog  limit,  8/>,  so  long  as  the  refer- 
ence is  to  the  interval  of  large  variation.  It  makes  no  difference  by 
what  radiation  the  nucleation  is  produced  (X-rays  or  other  radiation), 
8  7V/8  (8/)  is  rapidly  larger  as  the  intensity  of  ionization  is  greater, 
while  8/0  becomse  slowly  smaller  within  the  interval  in  question 
(Chapter  III,  figs.  49,  63  to  68).  Below  the  fog  limit  of  air  and 

*  Fog  limit  of  dust-free  air  just  exceeded. 

t  Including  loss  by  diffusion  or  other  time  loss. 


PERSISTENT  NUCLEI. 


135 


slightly  above  the  fog  limit  of  the  ionized  medium  the  following  data 
are  typical.  N^  shows  the  number  of  nuclei  caught  when  8/>  =  21 
cm.,  which  lies  within  the  pressure  interval  stated. 


=  4 

50       20.4  5  9 

25       20.3  10  (14) 

O          20.1  18  20 

f     200  20.3  10  16 

X-rays^      $°  (20.1)  22  (24) 

10  (19.7)  45  (33) 

5  19-6  50  36 

The  full  N  curves  are  best  given  graphically.  Data  for  the  radium 
at  D  =  100-200  cm.  are  scarcely  distinguishable  from  air  (fig.  68,  Chap- 
ter III)  except  near  the  fog  limit;  for  radium  at  D  —  10-25  cm-  they 
lie  close  together,  above  the  former  and  below  the  data  for  D  =  o. 
With  these,  the  X-ray  effects  at  D  —  10-50  are  in  sequence.  Thus 
there  is  general  continuity  between  the  air  curves,  the  radium  curves, 
and  the  X-ray  curves.  As  a  whole,  the  curves  for  D  and  %p  are 
doubly  inflected  ;  relatively  large  (efficient)  nuclei  are  rapidly  fewer 
in  number  as  §p  decreases  ;  relatively  small  nuclei  are  also  rapidly 
fewer  in  number  as  §p  increases.  Nevertheless  the  efficient  nuclei  of 
intermediate  dimensions  are  of  all  sizes,  while  this  size  tends  to  become 
more  uniform  as  the  ionization  is  greater,  i.  e.,  the  slopes  of  the  curves 
become  steeper.  Gradation  is  accentuated  for  the  case  of  weak  ioniza- 
tion. The  case  of  nonionized  air  is  shown  in  figs.  45,  46,  Chapter  III. 

The  efficiency  here  referred  to  depends  not  merely  on  the  apparatus 
(suddenness  of  exhaustion),  but  in  particular  on  the  degree  to  which 
larger  nuclei  are  present,  remembering  that  all  the  nuclei  in  question 
are  produced  in  dust-free  air.  As  the  nuclei  are  essentially  graded  in 
size,  the  larger  soon  capture  all  the  available  moisture  to  the  exclusion 
of  the  smaller,  and  the  coronal  diameter  ceases  to  increase  with  8/>. 
The  question  will  be  specifically  treated  elsewhere. 

93.  Persistent  nuclei.—  If  the  X-ray  bulb  is  approached  nearer  the 
fog  chamber,  or  if  a  more  efficient  bulb  is  used,  so  that  the  density  of 
the  ionization  within  the  fog  chamber  is  sufficiently  increased,  the 
rate  of  production  of  nuclei  will  eventually  exceed  the  rate  of  decay. 
(See  figs.  50,  51  ,  67,  84,  Chapter  III.)  Under  these  conditions  there  is 
not  merely  an  increase  of  number  in  the  lapse  of  the  time  of  exposure 
to  the  radiation,  but  essentially  an  increase  of  size,  i.  e.t  the  nuclei 
grow  indefinitely.  They  are  now  persistent  for  hours  after  the  radia- 
tion ceases.  The  number,  N,  per  cubic  centimeter  increases,  therefore, 
in  marked  degree  and  at  an  accelerated  rate  with  the  time  of  exposure, 
certainly  for  10  minutes  or  more,  barring  the  invariable  loss  of  efficiency 


136      NUCLEATION   OF  THE   UNCONTAMINATED   ATMOSPHERE. 

of  the  X-ray  bulb.  These  nuclei  are  large,  requiring  very  little  super- 
saturation  for  condensation,  and  are  much  like  any  ordinary  nuclei. 
They  are  pronouncedly  of  all  sizes,  and  the  initial  coronas  are  apt  to 
be  distorted  and  stratified  beyond  recognition.  Whirling  rains  (sec- 
tion 94)  and  fog  accompany  the  first  condensation.  While  small  nuclei 
occur  throughout  the  chamber,  the  end  near  the  bulb  is  at  first  the 
seat  of  growth,  which  gradually  extends  to  the  other  end,  as  I  have 
shown  elsewhere.*  The  following  two  series  of  data,  showing  the 
generation  and  decay  of  nuclei  in  question,  may  be  cited  as  illustra- 
tions. The  pressure  difference,  8p=  20  cm.,  is  much  below  the  fog 
limit  for  dust-free  air,  in  the  given  apparatus. 

Time  of  exposure o  5  10  20    60        120      180  sec. 

NXio~3 o  2  ii  10         80                 t(ioo)          t(5°°) 

Time  after  exposure..  o  36  85  240  minutes. 

NX  io~3 (100)  36  20  Vanishing. 

Hence  there  is  a  decay  of  one-half  in  10  minutes  and  of  one-fifth  in 
80  minutes,  or  the  degree  of  persistence  is  200  to  300  times  larger  than 
in  the  first  paragraph.  The  data  indicate,  moreover,  that  both  of 
these  extreme  types  of  nuclei  and  all  intermediate  types  now  occur 
together,  as  may  be  tested  by  changing  the  pressure  difference,  S/>,  on 
exhaustion.  (Cf.  fig.  51,  Chapter  III,  for  8p=  25.)  Intermediate  rates 
of  generation  and  decay  may  be  obtained  by  moving  the  bulb  nearer 
to  or  farther  from  the  end  of  the  fog  chamber.  Finally,  the  rates  at 
which  the  nuclei  and  the  ionization  severally  decay,  between  which 
it  would  be  difficult  to  distinguish  in  the  case  of  the  very  fleeting 
nuclei,  stand  in  sharp  contrast  with  the  persistence  of  the  nuclei  of 
the  present  paragraph. 

If  N  be  expressed  in  thousands  of  nuclei  per  cubic  centimeter,  and 
time  of  decay,  /,  in  seconds,  the  equation  \\N=a-\-bt  (for  which 
there  is  here  but  little  justification)  shows  that  £:=  0.000013,  over  2O° 
times  smaller  than  in  section  91.  (Cf.  fig.  50,  Chapter  III.) 

First  exhaustion  data  of  the  generation  of  persistent  nuclei  are  diffi- 
cult to  obtain,  because  the  coronas  soon  become  heavy  fogs,  distorted 
beyond  recognition,  and  the  fog  limits  variable  over  wide  limits,  often 
approaching  vanishing  smallness.  The  number  of  persistent  nuclei 
generated  varies  with  the  time  of  exposure  at  an  accelerated  rate,  as 
if  the  nuclei  themselves  assisted  in  the  generation.  (Cf.  section  100  ; 
also  fig.  84,  Chapter  III.)  For  instance,  at  8^=19.7  cm.,  after  the 
times  of  exposure,  1,2,3  minutes,  the  nucleations  were  N=  io-3  22,  77, 
(120),  respectively. 

*  American  Journ.  Sci.,  XIX,  175. 

t  Computed  from  second  exhaustion,  after  subsidence  of  the  dense  fogs  of  first. 


PERSISTENCE   ON  SOLUTION.  137 

94.  Fleeting  nuclei  become  persistent  on  solution— Origin  of  rain.— 
L,et  the  fog  chamber  be  exposed  to  radiation  for  a  few  seconds  and 
thereafter  exhausted  (8^=25)  as  usual.  Closing  the  exhaustion  cock 
and  allowing  only  time  enough  to  measure  the  first  corona,  let  the 
influx  cock  be  opened  and  the  fog  chamber  be  refilled  with  dust-free 
air.  The  (primary)  corona  observed  is  thus  dispelled  before  much 
subsidence  of  fog  particles  can  take  place,  though  the  rain  will  natu- 
rally drop  out.  If  the  fog  chamber  is  now  left  without  interference 
(the  radiation  having  been  cut  off  immediately  after  the  first  exhaus- 
tion) for  one  or  more  minutes  or  longer,  a  second  exhaustion  to  the 
stated  limits  will  show  a  large  (secondary)  corona  relatively  to  the 
primary  corona.  In  other  words,  relatively  many  of  the  fleeting 
nuclei  or  ions  caught  in  the  first  fog  have  persisted,  whereas  without 
condensation  they  would  have  vanished  at  once  after  the  radiation 
was  cut  off.  (Cf.  figs.  56-59,  Chapter  III.)  The  following  is  an 
example  of  data  bearing  on  this  point,  /  denoting  the  time  elapsed 
from  the  evaporation  of  the  first  corona  to  the  precipitation  of  the 
second,  N\  the  number  of  nuclei  in  the  first,  and  N^  the  number  in 
the  second  corona: 

Sees.  Sees.  Sees. 

t  = 60  120  300 

M  Xio-8= 53  27  53 

A72Xio~3= 16  7  15 

The  experiments  are  complicated  by  the  variable  X-ray  bulb  ;  but 
it  is  obvious  that  while  all  the  nuclei  would  have  vanished  in  a  few 
seconds  without  condensation,  about  one-fourth  (in  other  experiments 
more)  persist  indefinitely,  if  reevaporated  after  condensation  from  fog 
particles. 

This  result  has  an  important  bearing  on  the  whole  phenomenon  of 
condensation  and  nuclei.  Clearly  the  latter,  after  the  evaporation 
specified,  becomes  solutional  or  water  nuclei,  in  which  the  original 
fleeting  nucleus  or  ion  behaves  as  a  solute.  The  decreased  vapor 
pressure  due  to  solution  eventually  compensates  the  increased  vapor 
pressure  due  to  curvature,  after  which,  at  a  definite  radius,  evaporation 
ceases  and  a  water  nucleus  results.  Such  a  nucleus,  however  small, 
must  be  large  in  comparison  with  the  dissolved  ion.  Hence,  on  con- 
densation, the  water  nuclei  will  capture  the  moisture  soonest  and  grow 
largest.  Now,  in  any  exhaustion  about  one-eighth  of  the  fog  particles, 
/.  e. ,  those  which  are  smallest  and  whose  nuclei  have  been  caught  at 
the  end  of  the  exhaustion,  regularly  evaporate  into  the  larger  parti- 
cles to  a  residue  of  water  nuclei.  These  are,  then,  the  first  to  be 
caught  in  a  succeeding  exhaustion.  This  is  the  explanation  of  the 
rain  which  not  only  accompanies  all  coronas  in  dust-free  air,  but  is 


138      NUCXEATION   OF  THE  UNCONTAMINATED  ATMOSPHERE. 

often  dense.     It  is  also  an  explanation  of  those  indefinite  alternations 
of  large  and  small  coronas  (periodicity). 

Further  experiments  in  the  wooden  fog  chamber  showed  that  25  to 
50  per  cent  of  the  fleeting  nuclei  could  be  caught  and  made  stable  on 
solution.  The  mean  datum  of  all  results,  irrespective  of  the  time  inter- 
val (the  effect  of  which  within  a  few  minutes  is  probably  inappreciable), 
is  a  preservation  of  39  per  cent  on  reevaporation  of  the  originally 
fleeting  nuclei  from  the  fog  particles  condensed  on  them.  In  the 
absence  of  subsidence  of  fog  (which  can  not  here  be  allowed  for),  the 
result  would  be  larger.  In  the  glass  fog  chamber,  which  could  be 
made  rigorously  free  from  leakage,  but  in  which  the  subsidence  loss 
was  greater,  20  per  cent  persisted,  while  all  but  2  to  5  per  cent  were 
lost  in  one  minute  in  the  absence  of  solution.  Persistence  in  the  i  to 
3  minutes  following  evaporation  was  not  appreciably  different,  indicat- 
ing long  periods  of  decay.  (Cf.  fig.  60,  Chapter  III.) 

95.  Solutional  enlargement  of  the  nuclei  of  dust-free  air. — The  most 
interesting  case  observed  is  the  marked  decrement  of  the  fog  limit  of 
dust-free  air  producible  by  solution  of  the  nuclei.      (Cf.  figs.  61,  62, 
Chapter  III.)     Let  the  first  exhaustion  be  made  decidedly  above  the 
fog  limit,  ftp  =22  cm.  (say  here  at  8/>  =  23  cm.),  to  obtain  a  corona  of 
appreciable  size.  On  evaporating  the  fog  particle,  let  the  second  exhaus- 
tion be  made  decidedly  below  the  fog  limit  (say  at  &p  =  2i  cm.).     A 
large  corona,  which  would  otherwise  be  quite  absent,  will  be  observed. 
Within  3  minutes  about  25  per  cent  of  the  nuclei  are  found  to  persist 
After  ic  minutes  not  more  than  50  per  cent  were  left.      Whether, 
without  solution,  air  nuclei  are  possibly  evanescent,  and  therefore 
maintained  by  some  penetrating  radiation,  remains  to  be  seen.     It 
should  be  recalled  that  the  nuclei  in  question  are  small,  even  as  com- 
pared with  ions. 

96.  Water  nuclei— Solutional  nuclei  in  general.— Apart  from  the 
functions  suggested  in  sections  94  and  98,  it  is  clear  that  the  water 
nucleus  must  play  an  important  part  throughout  all  phenomena  in 
nucleation.     It  seems  probable  that  immediately  after  exhaustion  pre- 
cipitation takes  place  on  all  nuclei,  large  and  small,  within  the  scope 
of  the  pressure  difference  applied.     The  smaller  fog  particles  then  at 
once  begin  to  evaporate  until  the  decrement  of  vapor  pressure,  due  to 
increasing  concentration  of  the  solution,  is  equivalent  to  the  incre- 
ment of  vapor  pressure  due  to  decreasing  size,  whereupon  evaporation 
ceases.     This  is  the  condition  of  persistence  of  a  water  nucleus,  the 
ultimate  size  of  which  depends  on  the  original  strength  of  the  solu- 


SOLUTION  AL   NUCLEI   IN   GENERAL.  139 

tion  partially  evaporated.  Clearly  the  water  nucleus  is  always  larger 
than  the  original  nucleus  which  it  holds  in  solution. 

Phenomena  of  the  present  kind  may  be  examined  by  identically 
agitating  solutions  of  different  bodies  in  different  solvents  and  of  differ- 
ent strengths,  beginning  with  the  pure  solvent.  This  may  be  water 
or  any  other  volatile  liquid.  The  number  of  nuclei  obtained,  cat. 
par.,  varies  both  with  the  solvent  and  the  solute.  Thus  on  shaking 
i  per  cent  solutions  identically  and  computing  the  number  of  nuclei, 
N,  from  the  coronas  observed  in  each  case  the  following  data  were 
found  :  Pure  water,  A^=  130 ;  organic  bodies  dissolved  in  water  (su- 
crose, glucose,  glycerin,  urea,  etc.),  N=6oo-,  mineral  salts  dissolved 
in  water  (nitrates,  chlorides,  sulphates,  etc.),  N=  1,300;  naphthalene 
dissolved  in  benzol,  TV— 3,500 ;  paraffin  in  benzol,  ^=5,000.  A 
definite  demarcation  of  groups  is  thus  apparent,  but  it  is  difficult  to 
even  conjecture  an  explanation. 

If  the  solvent  is  pure,  the  nuclei  produced  by  shaking  are  exces- 
sively fleeting,  a  result  attributable  to  their  relatively  small  size.  As 
the  concentration  increases  for  a  given  solvent,  persistence  increases 
with  the  number  of  nuclei  produced. 

If  the  absorption  per  second  takes  place  ct  the  walls  of  the  vessel  as 
the  first  power  of  the  number  of  nuclei  present,  the  following  constants 
(k)  show  the  character  of  the  phenomena: 

Pure  water £  =  5-10 

Inorganic  saline  solutions i  percent £  =  0.05 

o.oi      percent &  =  o.o8 

o.oooi  percent k  =  z 

Neutral  organic  solutes  in  water i  percent k  =  o.2 

o.oi      percent k  =  o.6 

Neutral  liquid  organic  solutes  in  water. i  per  cent k  =  1.2 

o.oi      percent £  =  2.4 

Solid  hydrocarbons  in  liquid  hydrocarbons,  i percent k  =  o.O2  to  0.04 

When  the  solvent  is  a  hydrocarbon,  etc.,  the  fog  particles  are  rela- 
tively large  as  compared  with  the  water  particles  (c<zt.  par.).  Hence  the 
coronas  remain  normal  (white-centered  and  showing  the  usual  diffrac- 
tion pattern)  even  when  the  nuclei  are  present  in  millions  per  cubic 
centimeter.  These  coronas,  moreover,  are  intensely  brilliant,  and 
but  for  the  difficulty  in  keeping  the  heavy  vapors  saturated,  they 
would  offer  exceptionally  good  conditions  for  the  measurement  of 
nucleations.  Again,  the  exhaustion  method  is  available  for  investigat- 
ing the  diffusion  of  the  heavy  vapors  into  nucleated  air.  Finally, 
sulphuric -acid  nuclei,  sulphur  and  sulphide  nuclei  (oxidizable  to  sul- 
phates) are  probably  a  special  class  of  water  nuclei  which  are  stable 
because  they  contain  an  intensely  hygroscopic  solute. 


140      NUCLEATION   OF  THE   UNCONTAMINATED   ATMOSPHERE. 

97.  Alternations  of  large  and  small  coronas— Periodic  distributions 
of  efficient  nuclei  in  dust-free  air. — The  coronas  in  question  may  be 
distinguished  as  superior  and  inferior  coronas.  They  are  obtained  in 
successive  exhaustions  of  dust-free  air,  under  conditions  of  experiment 
which  are  quite  identical,  filtered  air  being  introduced  in  the  periods 
between  the  exhaustions,  after  all  the  fog  particles  have  subsided. 
The  efficient  nuclei  are  therefore  present  in  large  and  small  number, 
alternately,  usually  in  the  ratio  of  about  8  to  i.  Figures  14  and  15, 
Chapter  II,  give  an  example  of  the  changes  of  angular  coronal  diam- 
eter, 5,  in  the  successive  observations  with  dust-free  air  enumerated 
by  the  abscissas.  The  pressure  difference  is  8/>  =  3i  cm.  and  the 
time  between  the  exhaustions  2  minutes.  Twenty  exhaustions  are 
recorded,  but  the  experiment  might  have  been  prolonged  indefinitely. 
In  figure  17,  Chapter  II,  there  are  3 -minute  periods  between  the 
exhaustions.  In  figure  18  the  periods  are  5  minutes  in  length,  but  the 
phenomenon  here  vanishes.  All  the  graphs  show  that  relatively  high 
inferior  coronas  (h)  are  followed  by  relatively  low  (/)  superior  coronas, 
and  low  inferior  coronas  are  followed  by  relatively  high  superior 
coronas;  furthermore,  that  coronas  of  mean  aperture  are  followed  by 
coronas  of  the  same  kind,  so  that  the  periodicity  ceases,  as  seen  in 
figures  1 6  and  18  of  Chapter  II.  In  figure  16  alternations  and  steady 
aperture  were  obtained  under  otherwise  like  conditions.  In  figure  26 
the  same  phenomenon  is  exhibited  in  case  of  dust-free  air  energized 
by  weak  radium.  The  ordinates  here  show  the  number  of  nuclei  per 
cubic  centimeter,  so  that  the  sweep  of  the  alternations  is  more  striking. 

An  explanation  of  these  phenomena  may  be  given  (sections  96,  98) 
in  terms  of  the  occurrence  of  water  nuclei  produced  by  the  evaporation 
of  the  small  fog  particles  to  a  size  at  which  solutional  decrement  of 
vapor  pressure  balances  the  increment  due  to  increased  curvature. 
In  figures  14  and  15,  Chapter  II,  the  average  inferior  nucleations  of 
dust-free  air  are  about  12,000,  the  average  superior  nucleations  over 
90,000,  so  that  explanations  in  terms  of  negative  and  positive  ions  are 
out  of  the  question. 

To  precipitate  nuclei  which,  as  is  usual,  are  more  or  less  graded  in 
size,  in  a  single  exhaustion,  must  be  generally  impossible  for  similar 
reasons.  While  temperature  after  exhaustion  approaches  its  original 
isothermal  value,  the  small  particles  caught  at  the  end  of  the  exhaus- 
tion to  the  amount  of  about  10  per  cent  of  the  total  number  evaporate 
to  the  water  nuclei  stage,  to  be  precipitated  in  the  next  exhaustion. 
This  evaporation  probably  accounts  for  the  permanence  of  coronas 
throughout  the  period  of  subsidence  of  fog  particles,  during  the  early 
stages  of  which  temperature  rapidly  increases. 


PERIODICITY. 

98.  Cause  of  periodicity.—  In  cases  of  large  and  small  coronas, 
whether  the  persistence  be  attributed  to  electrical  potential  or  to  solu- 
tion, a  water  nucleus  is  always  in  question.  Small  fog  particles  are 
caught  on  small  nuclei  near  the  limit  of  exhaustion  and  these  evapo- 
rate and  become  the  water  nuclei  available  for  the  next  exhaustion. 
In  general,  there  are  three  groups  of  nuclei  (x,y,  z)  concerned  in  any 
exhaustion  :  A  group,  x,  of  water  nuclei  form  the  preceding  exhaustion; 
a  group,  zt  which  will  evaporate  to  make  the  water  nuclei  of  the  suc- 
ceeding exhaustion  ;  finally,  the  group  y,  comprising  nuclei  adapted 
to  become  the  efficient  nuclei  of  the  exhaustion  in  question. 

In  case  of  periodicity  the  successive  exhaustions  follow  the  scheme— 

Exhaustion  i  y\  z\  Superior  corona  on  y\ 

2  xz  =  z\  -  z%  =  o  Inferior  corona  on  z\ 

3  xs  =  Z2  =  o  yz~{-ys  ^3  Superior  corona  on  ja  +  Js 

4  x±  =  £3  2-4  =  0  Inferior  corona  on  z$ 

5  Xb  =  z±  =  o  yi-\-y*>  z<b  Superior  corona  on  y±  -f-  y$ 

All  the  details  observed  with  alternations  are  thus  explained.  In 
view  of  the  rapidity  of  decay,  the  corona  will  be  formed  on  the  satura- 
tion Value 


99.  Persistence  in  general.—  This  may  reasonably  be  ascribed  to  the 
formation  of  water  nuclei,  a  point  of  view  carried  out  in  my  memoir 
on  the  structure  of  the  nucleus  (Smithsonian  Contributions,  No.  1373, 
vol.  29,  1903),  but  much  enhanced  by  the  data  of  the  present  inves- 
tigation .     The  heavy  rains  accompanying  condensation  in  case  of  the 
persistent  X-ray  nuclei  are  attributable  to  spontaneous  condensation 
without  supersaturation,  the  nucleus  acting  under  intense  X-radiation 
like  a  hygroscopic  solute.     The  same  result  may  follow  the  action  of 
ultraviolet  light,  as  it  certainly  must  result  from  the  presence  of  phos- 
phorus and  of  sulphuric-acid  nuclei. 

100.  Secondary  generation.  —  This  is  a  curious  phenomenon,  show- 
ing that  the  decaying  persistent  nucleus  produced  by  the  X-rays  is 
apparently  radio-active,  or  that  the  walls  of  the  fog  chamber  are  so, 
or  else  that  the  large  nuclei,  if  left  without  interference,  break  into  a 
number  (on  the  average  about  three)  of  smaller  nuclei,  whereby  the 
nucleation  is  actually  increased  in  the  lapse  of  time  after  exposure. 
In  other  words,  if  the  nucleation  is  observed  without  cutting  off  the 
radiation  in  one  case,  and  if  in  the  second  case  the  nucleation  iden- 
tically produced  is  observed  at  a  stated  time  after  the  radiation  has 
ceased,  the  number  in  the  latter  case  (anomalously  enough)  is  in 
excess.    (Cf.  fig.  70-76,  Chapter  III.)    The  following  examples  make 
this  clear,  the  X-ray  bulb  being  5  cm.  from  the  fog  chamber,  and  the 


142      NUCLEATION   OF  THE  UNCONTAMINATED   ATMOSPHERE. 

exhaustion  carried  to  §p  —  20  cm.  These  data  are  computed  from  the 
second  exhaustions,  as  the  first  show  the  densely  stratified  fogs  un- 
available for  measurement. 

Rays  on  ..........     2       2       2       2       2       2       2       2       2  minutes. 

Rays  off  ..........     o       4       o       4       o       2       020       o  minutes. 

""3  .........   20     52     20     32     25     30     13     34     30 


With  the  bulb  at  different  distances  from  the  fog  chamber,  the  fol 
lowing  data  admit  of  the  same  interpretation  (figs.  74,  76): 


Distance,  D=      5     10     15 

Rays  on 2       2       2 

Rays  off o       o       o 


5     10     15  cm. 
222  minutes. 
222  minutes. 


58       9       i 

The  phenomenon  vanishes  when  the  radiation  is  too  weak  to  produce 
persistent  nuclei ,  therefore,  either  when  the  bulb  loses  efficiency  or 
when  it  is  too  far  from  the  fog  chamber. 

101.  Space  surrounding:  the  X-ray  tube  a  plenum  of  radiations.— 

While  the  phosphorescent,  photographic,  and  electric  effects  of  X-radia- 
tion  decrease  rapidly  with  the  distance,  D,  from  the  tube,  the  nucleat^ 
ing  effect  (N,  nuclei  generated  per  cubic  centimeter,  instantly)  is  nearly 
constant  over  relatively  enormous  distances.*  (Cf.  fig.  69,  Chapter 
III.)  Thus  to  give  two  examples  among  many  (8p=2$  cm.): 


D  — 6     200     600 

88     83       83 


6     200     600  cm. 
79       79       79 


The  laws  of  inverse  squares  would  predicate  a  reduction  of  10,000  to 
i  between  these  limits  ;  and,  in  fact,  at  6  cm.  the  phosphorescent 
screen  is  intensely  luminous,  at  200  cm.  very  dim,  at  600  cm.  quite 
dark,  as  in  the  case  of  any  ordinary  illumination.  The  leaves  of  an 
electroscope  within  a  glass  bell  jar  collapse  in  a  time  which  is  directly 
as  the  square  of  the  distance  from  the  energized  X-ray  bulb.  The 
result  obtained  with  nuclei  is  astonishing ;  the  nuclei-producing 
radiation  would,  at  first  sight,  seem  to  be  of  an  extremely  penetrating 
kind,  akin  to  the  gamma  rays  of  radium,  and  distinct  from  the  ordi- 
nary phosphorescence-producing  X-rays.  This  impression  is  accen- 
tuated by  the  fact  that  the  radiation  can  not  be  stopped  by  lead  screens 
many  centimeters  in  thickness,  placed  between  bulb  and  fog  chamber. 
(Cf.  figs.  79,  81,  82,  83,  Chapter  III.)  The  following  are  typical  ex- 
amples, in  which  the  distance  between  the  lead  plates  screening  the  fog 
chamber  and  the  X-ray  tube  is  D=6oo  and  200  cm.,  respectively.  N 

*  Supposing  that  the  fog  chamber  is  not  inclosed  in  impervious  metal.  In  the  latter 
case,  with  the  lead  covering  open  toward  the  X-ray  bulb  only,  there  is  constancy  of  N 
within  20  per  cent  over  6  meters. 


SECONDARY   RADIATION. 

shows  the  number  of  nuclei  instantly  generated  behind  the  lead  plates 
in  the  two  cases. 

Thickness  of  lead  screen o      0.14       0.28       0.56      0.84       1.12     o  cm. 

D  —  600  cm.     A^Xio-3 67     28          28          31          29          31        76 

D  —  200  cm.     NX  icr3 79    44          48          41  44       70 

Again,  the  X-ray  bulb  apparently  emits  this  radiation  forward  as 
well  as  rearward,  as  if  the  thin  anticathode  were  quite  pervious.  I 
found,  for  instance,  for  the  radiation  of  the  anticathode  at  6  meters 
from  the  fog  chamber — 

From  the  front  face  (tube  directed),  NX  io~3  =  42 
From  the  rear  face  (tube  reversed),  N  X  io~3  =  35 

or  8 1  per  cent  of  the  former  apparently  issues  from  the  rear  face  (fig. 
80,  Chapter  III).  Even  the  reversal  of  the  current  does  not  stop  the 
radiation,  for  about  16  per  cent  of  the  normal  intensity  is  still  radiated 
when  the  concave  mirror  is  made  the  anode  (fig.  80,  Chapter  III). 

The  total  efficient  radiation  may  be  reduced  to  a  limit  by  lead  screens 
a  few  millimeters  in  thickness,  or  less  ;  thereafter  it  can  not  be  further 
reduced  by  lead  screens  many  centimeters  in  thickness.  For  instance, 
when  the  radiation  comes  from  600  cm.,  a  single  lead  plate  (thickness 
0.14  cm.)  is  more  than  sufficient  to  reduce  the  effective  radiation  to  a 
minimum,  which  amounts  to  (somewhat  less  than)  one-half  of  the  total 
intensity,  at  least  when  estimated  in  terms,  of  the  number  of  nuclei 
produced.  (Figs.  81,  83,  Chapter  III.)  If  the  nucelation  comes  from 
200  cm.,  one  plate  has  the  same  effect,  even  though  a  thickness  of  400 
cm,  of  air  has  been  removed.  The  thickness,  0.14  cm.,  is  more  than 
enough  to  reduce  the  radiation  to  the  limit  in  question.  This  again 
amounts  to  a  little  more  than  one-half  the  total  intensity.  (Fig.  82, 
Chapter  III.)  At  a  distance  of  5  cm.  no  more  plates  may  be  needed; 
but  the  conditions  are  now  too  complicated  to  be  described  here, 
chiefly  because  persistent  nuclei!  are  producible.  Moreover,  80  per 
cent  of  the  total  intensity  may  ultimately  escape  absorption.  Thus 
the  rays  from  different  distances  behave  alike  for  the  more  pervious 
media  and  in  relation  to  very  dense  screens.  (Fig.  83,  Chapter  III.) 

102.  Lead-cased  fog  chamber.— To  interpret  these  surprising  results 
it  will  be  necessary  to  surround  the  fog  chamber  with  a  casket  of  lead, 
having  a  lid  on  the  side  fronting  the  X-ray  bulb  ;  for  even  though  the 
lead  plates  above  may  efficiently  cut  off  the  primary  rays,  they  would 
leave  the  secondary  radiation  free  to  enter  laterally  through  the  broad- 
sides of  the  fog  chamber.  When  this  was  done  the  results  reduced 
the  penetrability  of  lead  to  a  more  reasonable  figure,  as  may  be  seen 


144      NUCIvEATlON  OF  THE  UNCONTAMINATED  ATMOSPHERE. 

from  the  following  example  of  results  when  the  distance  between  bulb 
and  fog  chamber  was  2  meters  : 

Thickness  of  lead  penetrated=     o      0.14    0.28     0.42  cm. 
N  X  icr3  ....................  77     10          7          5 

i.  e.,  14,  9,  and  7  per  cent  of  the  total  intensity  passes  one,  two,  and 
three  plates,  respectively.  (Figs.  77,  78,  Chapter  III.)  A  glass  plate, 
7  mm.  thick,  and  an  iron  plate,  0.5  mm.  thick,  allowed  about  90  per 
cent  to  pass  ;  when  the  casket  was  left  open,  and  the  lead  plate  placed 
near  the  bulb,  17  per  cent  of  the  total  radiation  was  effective,  the 
excess  being  of  secondary  origin.  The  passage  through  a  plate  of 
tinned  iron  (cf.  figs.  85,  86,  Chapter  III)  may  be  observed  for  a  bulb 
6  meters  distant,  as  follows  : 

Thickness  of  plate  ----     o      0.05      o.io    0.20  cm. 
............   36    28    "      ii          7 


It  follows,  then,  that  in  the  above  examples  (101)  nearly  one-half  of 
the  total  radiation  was  derived  from  secondary  sources,  since  the  pri- 
mary radiation  was  certainly  stopped  off  to  within  10  per  cent  by  the 
lead  plates.  To  the  eye  of  the  fog  chamber,  therefore,  the  walls  of 
the  room  are  aglow  with  radiation,  and  no  matter  in  what  position  the 
bulb  may  be  placed  (observationally  from  6  cm.  to  6  m.  between  bulb 
and  chamber),  the  X-illumination,  as  derived  from  primary  and  sec- 
ondary sources,  is  constant  everywhere.  It  is  to  be  understood  that 
the  X-illumination  here  referred  to  may  be  corpuscular.  In  fact,  so  far 
as  I  see,  the  primary  and  secondary  radiation  here  in  question  may  be 
identical  ;  for  the  corpuscles  may  come  from  the  circumambient  air 
molecules  shattered  by  the  shock  of  gamma  rays. 

The  fog  chamber,  if  open  at  the  end  toward  the  bulb,  shows  the 
same  total  intensity  ;  but  in  such  a  case  the  inner  walls  of  the  casket, 
etc.,  become  the  source  of  secondary  rays. 

The  behavior  of  the  wooden  fog  chamber  in  relation  to  rays  coming 
from  different  distances  being  such  as  if  the  circumambient  medium 
were  equally  energized  with  something  recalling  the  character  of  gal- 
vanic polarization  throughout,  the  following  mean  data  are  designed 
to  throw  further  light  upon  this  behavior  (fig.  69,  Chapter  III). 

Fog  chamber  ..........................  D  —   6      50     200     600  cm. 

Wood,  lead-cased  .......................    lo"3  N=  50  50      38 

Glass,  walls  0.3  cm.,  bottom  i  cm.  thick.... 

1  55  34       *4 

Glass,  cased  in  close-fitting  lead  tube,  pro- 
longed 50  cm.  toward  bulb  ............  —   *  52       25       12 

Media  pervious  with  difficulty  eliminate  the  secondary  radiation  enter- 
ing the  broadsides  of  the  fog  chamber,  and  to  close  the  end  toward 


GAMMA   RAYS. 


145 


the  bulb  is  to  eliminate  nearly  all  the  rays  (figs.  77,  78,  Chapter  III) ; 
but  if  this  is  open,  the  number  of  nuclei  instantly  generated  decreases 
much  more  slowly  than  the  first  power  of  distance.  The  fact  that  to 
the  very  pervious  wooden  fog  chamber  the  medium  within  a  sphere  of 
at  least  6  meters  in  radius  remains  almost  equally  energized  through- 
out remains  a  result  of  importance. 

103.  Possibility  of  two  kinds  of  radiation  from  the  X-ray  tube.— It  has 
been  shown  that  for  very  short  exposures  (sections  101  and  102)  the 
nucleation  is  the  same,  whether  the  bulb  is  placed  at  6  cm.  or  6  m. 
from  the  fog  chamber.     But  only  in  the  former  case  (D=6  cm.)  is  the 
effect  cumulative  ;  only  for  very  short  distances  will  persistent  or  very 
large  nuclei  appear  if  the  exposure  is  prolonged  several  minutes.     I 
have,  therefore,  suspected  that  the  radiation  from  the  X-ray  bulb  is 
twofold  in  character ;  that  the  instantaneous  effect  (fleeting  nuclei)  is  due 
to  a  gamma-like  ray,  quick  moving  enough  to  penetrate  several  milli- 
meters of  iron  plate  appreciably  even  for  £>=6  meters  ;  furthermore, 
that  the  cumulative  effect  (persistent  nuclei)  is  due  to  X-light,  properly 
so  called,  which  produces  the  usual  effects  subject  to  the  laws  of  inverse 
squares ;  but  it  is  noteworthy  that  while  the  penetration  of  X-rays 
is  relatively  small,  and  the  distance  effect  negligible  (section  101),  they 
are  both  large  for  the  radiation  from  radium  (section  104). 

104.  Nucleation  due  to  gamma  rays. — To  what  extent  nucleation  is 
producible  by  gamma  rays  may  be  tested  by  radium  inclosed  in  a 
thick  chamber  of  lead.      The  results  are  strikingly  comfirmatory. 
(Figs.  87  to  89,  Chapter  III).     For  instance,  in  case  of  10  mg.  of 
radium  (io,oooX)  inclosed  in  a  hermetically  sealed  alumimum  tube  and 
placed  outside  but  close  to  the  end  of  the  fog  chamber  (bottom  nearly 
i  cm.  thick,  walls  0.3  cm.  thick),  the  data  were  (fig.  89,  Chapter  III)  : 

Radium  in  sealed  aluminum  tube icT3jV=  27     Transmission  100 

Radium  in  lead  tube  0.5  cm.  thick 23  85 

Radium  in  lead  tube  i  cm.  thick 18  69 

The  nuclei  are  thus  very  largely  due  to  this  extremely  penetrating 
radiation.  By  using  lead  tubes,  capped  and  not  capped,  30  cm.  and 
60  cm.  long,  and  placed  parallel  to  the  fog  chamber  and  in  contact 
with  its  sides,  no  evidence  of  secondary  radiation  was  discernible,  the 
effective  radiation  passing  through  the  lead  walls  as  specified. 

In  comparison  with  the  abundant  nucleation  after  the  penetration 
specified,  the  decrease  of  nucleation  observed  when  the  tube  is  at  dif- 
ferent distances,  D,  from  the  fog  chamber  is  remarkably  large.  For 
example  (fig.  90,  Chapter  III), 

D  =   o    10    30    50     loo    200  cm. 
WXio~*=30     13      8       5        3        2 

*  Through  0.14  cm.  of  lead  icr*  N=  3 ;  through  0.05  cm.  of  iron  lo"8  N=  44. 


146     NUCLEATION  OF  THE  UNCONTAMINATED  ATMOSPHERE. 

If  measurement  be  made  from  the  line  of  sight  (10  cm.  from  the  ends 
of  the  fog  chamber),  the  nucleation  decreases  less  rapidly  than  the  first 
power  of  distance.  Hence,  whereas  the  distance  effect  in  case  of 
X-rays  is  small,  it  is  very  large  in  case  of  radium.  On  the  other  hand, 
rays  from  radium  show  remarkable  nucleating  power  after  penetrating 
many  centimeters  of  lead,  whereas  the  nucleating  power  of  the  X-rays 
after  such  penetration  is  relatively  negligible.  (Figs.  69  and  78,  89 
and  90,  Chapter  III.) 

105.  Distribution  of  nucleation  within  the  fog  chamber— Radium.— 

Finally,  when  the  rays  have  once  entered  the  fog  chamber,  the  nuclea- 
tion along  the  axis  seems  nearly  uniform.  Measurements  are  diffi- 
cult ;  but  while  the  nucleation  decreases  nearly  to  one-fourth  when 
the  radium  is  placed  on  the  outside  of  the  fog  chamber,  40  cm.  axially 
from  the  end,  the  coronas  along  40  cm.  within  the  fog  chamber  are 
nearly  of  the  same  aperture  for  any  given  position  of  the  radium  tube. 

106.  Distribution  of  nucleation  within  the  fog  chamber— X-rays.— 

Obviously  when  the  X-ray  bulb  is  at  a  distance  from  the  fog  chamber 
and  the  nuclei  fleeting,  they  will  be  uniformly  distributed  within  the 
chamber,  being  everywhere  at  saturation  density  for  the  given  inten- 
sity of  radiation. 

The  conditions  are  far  different,  however,  when  the  bulb,  as  in  figure 
i ,  Chapter  I,  is  near  the  chamber  and  the  nuclei  persistent.  In  such  a 
case,  if  we  distinguish  between  the  A  and  the  B  sides  of  the  fog  chamber 
(where  A  is  nearer  the  bulb),  and  if  we  use  a  pressure  difference,  Spt 
decidedly  below  the  fog  limit,  8/>0,  of  dust-free  air,  the  nuclei  within  the 
given  range  of  condensation  are  for  short  times  of  exposure  found  on 
the  A  side  only.  The  coronas  are  relatively  small  in  size,  roundish, 
decreasing  in  aperture  to  a  vanishing  angular  radius  from  the  bulb  end 
of  the  chamber  toward  the  middle.  Beyond  this,  on  the  right,  nuclei 
are  too  small  to  respond  to  the  given  pressure  difference,  $p,  and  the  B 
side  remains  clear  on  exhaustion.  Asthe  time  of  exposure  to  the  X-radia- 
tion  is  increased  from  i  to  10  minutes,  the  nucleation  of  the  A  side 
becomes  denser,  coarser,  and  nonuniform  in  distribution,  vertically  as 
well  as  horizontally,  while  the  efficient  nuclei  are  found  in  continually 
increasing  numbers,  and  at  greater  distances  on  the  B  side,  until  they 
eventually  occur  throughout  the  chamber.  The  growth  of  the  coronas 
seen  on  the  first  exhaustion  after  successively  increasing  times  of 
exposure  show  a  characteristic  sequence  of  types  (figs.  2-6,  Chapter  I), 
as  they  pass  (when  seen  through  plate-glass  apparatus)  from  roundish 
to  oval,  spindle-shaped,  gourd-shaped  with  a  long  serpentine  neck, 


DISTRIBUTION   WITHIN   FOG   CHAMBER.  147 

and  finally  wedge-shaped  forms,  showing,  therefore,  continued  sym- 
metry about  the  middle  horizontal  plane  or  plane  of  vision,  in  spite  of 
the  whirling  rains  and  densely  stratified  fogs  which  accompany  the 
advanced  condensations.  The  design  lasts  but  an  instant,  for  although 
the  nuclei  may  be  suspended  in  accordance  with  the  given  distribution, 
this  is  not  possible  for  the  heavy  fog  particles  after  condensation. 

These  phenomena  bear  fundamentally  on  the  origin  of  persistent 
nuclei,  and  these  are  obviously  graded  in  size,  decreasing  from  the  A 
to  the  B  sides,  as  well  as  from  the  middle  plane  toward  the  top  and 
bottom  of  the  fog  chamber.  With  regard  to  the  latter  or  horizontal 
symmetry,  moreover,  the  distortion  is  such  that  the  fog  particles  must 
increase  in  size,  from  the  plane  of  symmetry  down  and  up. 

If  the  gradation  is  linear,  for  instance,  with  a  coefficient,  a,  so  that 
d—d^—ah)  where  d  is  the  diameter  of  fog  particle  at  a  height  or  a 
depth,  h,  from  the  plane  of  sight,  and  £  the  radius  vector  from  the 
coronal  center  to  a  locus  of  uniform  color,  a,  the  angle  of  s  with  the 
horizontal, 


s  =  —  (Xo/siu  a)  (i  —  |/i  +  2asQ  sin  a/^0). 

These  curves  are  campanulate  in  outline,  passing  from  closed  roundish 
to  open  basin-shaped  forms,  and  two  examples,  a  and  a!  ,  are  shown  in 
figure  7,  Chapter  I.  They  all  intersect  at  b  and  c,  and  the  ends  lying 
outside  these  lines  may  obviously  here  be  ignored.  As  the  march 
from  a  to  a'  is  one  of  intensified  gradation,  the  curves  eventually 
becoming  flat,  it  is  clear  that  the  horizontal  symmetry  of  figures  2  to  6 
is  suggested.  The  latter  contain,  in  addition,  the  essential  gradation 
from  left  to  right,  due  to  the  position  of  the  bulb. 

10  1.  Origin  of  persistent  X-ray  nuclei.  —  Admitting  that  the  fog  parti- 
cles are  larger  from  the  middle  plane  toward  the  top  and  bottom  of 
the  fog  chamber,  the  nuclei  must  either  be  large  in  size  toward  the 
top  and  bottom  as  well  as  toward  the  bulb,  or  they  must  be  smaller  in 
number.  The  latter  case  may  be  dismissed.  It  follows,  then,  that  the 
layers  of  stagnant,  originally  dust-free,  air  within  the  chamber  become 
more  and  more  rich  in  relatively  large  nuclei  as  they  lie  nearer  the 
top  and  bottom  and  the  end.  (The  corresponding  effect  toward  and 
from  the  line  of  sight  will,  of  course,  remain  invisible.)  These  large 
nuclei  capture  nearly  all  the  moisture  in  the  parts  in  question,  giving 
rise  to  the  whirling  rains  and  dense  fogs  after  condensation,  whereby 
the  essentially  unstable  character  of  this  distribution  is  made  manifest. 

Hence  the  case  is  such  as  if  the  persistent  nuclei  were  generated  by 
the  impact  of  the  X-rays  of  sufficient  intensity  on  solid  and  liquid  parts 


148     NUCLEATION   OF  THE  UNCONTAMINATED  ATMOSPHERE. 

of  the  vessel,  recalling  the  way  in  which  similar  nuclei  are  produced  by 
ignition  and  by  high  electrical  potential,  etc.  Or  one  may  state  that 
the  secondary  X-radiation,  which  plays  near  the  walls  of  the  vessel,  is 
particularly  intense  near  those  walls,  so  that  the  growth  of  nuclei  in 
the  field  of  ionized  air  adjoining  is  most  rapid  near  those  parts.  In 
any  case  the  number  of  efficient  nuclei  near  the  horizontal  plane  of 
symmetry  is  apparently  large,  because  these  nuclei  are  nearly  of  a  size 
and  all  are  therefore  available  for  condensation.  The  number  of 
efficient  nuclei  near  the  walls  is  smaller  because  large  and  small  nuclei 
are  here  intermixed,  and  the  former  capture  nearly  all  the  moisture  in 
those  parts.  The  actual  nucleation  here  must,  however,  be  exceed- 
ingly large,  and  it  is  because  of  the  relatively  great  density  of  the 
nucleation  in  question  that  rapid  and  pronounced  growth  of  nuclei 
become  possible. 

Thus  there  must  be  many  nuclei  which  fail  of  capture  in  the  first 
exhaustion,  and  for  this  reason,  finally,  the  coronas  on  second  (other- 
wise identical)  exhaustion,  without  fresh  nucleation  or  exposure  to 
the  X-rays,  are  invariably  phenomenally  large  and  may  correspond  to 
one-third  or  one-half  as  many  nuclei  per  cubic  centimeter  as  the  first 
coronas. 

108.  Order  of  size  of  persistent  X-ray  nuclei, — This  may  be  expressed 
in  terms  of  the  pressure  difference  needed  to  produce  condensation. 
Unfortunately  the  coronas  on  first  exhaustion  are  apt  to  be  distorted 
or  dense  fogs,  while  as  the  pressure  difference,  Bp,  decreases  they 
become  more  and  more  diffuse  and  equally  unsuitable  for  measure- 
ment. I  have,  therefore,  computed  the  'number  of  particles,  N2, 
present  on  second  exhaustion  for  a  given  nucleation .  These  coronas 
are  smaller,  but  sharp,  and  the  fog  particles  are  condensed  on  the  water 
nuclei  resulting  from  the  first  exhaustion.  One  may  estimate  roughly 
that  about  10  per  cent  of  the  original  number  of  nuclei  are  condensed 
in  this  way.  The  following  is  an  example  of  results  for  3-minute 
intervals  of  exposure  to  the  X-rays  (curves  38,  39,  Chapter  II)  : 

SP=33     25     17       9       4     17 
JV9Xiors=i5     46     47     28     14     46 

The  passage  through  a  maximum  at  Sp=  16-20  is  capable  of  a  variety 
of  explanations,  and  therefore  of  little  interest.  The  important  point 
at  issue  is  the  fact  that  these  nuclei  require  almost  no  supersaturation 
for  condensation .  Filmy  coronas  are  produced  by  vanishing  pressure 
differences.  It  follows,  then,  that  these  nuclei  are  about  of  the  size 
of  ordinary  dust-like  nuclei. 


STRUCTURE   OF   DUST-FREE   AIR.  149 

109.  Ordinary  nuclei.— The  persistent  nuclei  of  section  108  were  pro- 
duced by  radiation  in  a  medium  of  damp  air,  with  the  specific  object  of 
avoiding  the  introduction  of  foreign  matter  into  the  fog  chamber.     It 
is  well  known,  however,  that  nuclei  are  producible  by  any  profound 
method  of  trituration  which  may  be  mechanical,  as  in  the  comminu- 
tion of  water  by  agitation  or  by  the  impact  of  jets.     The  resources 
used  may  be  of  a  more  refined  physical  character  like  ignition  or  high 
electrical  potential,  or  of  a  chemical  character  like  combustion  and 
the  slow  oxidation  of  phosphorus,  etc.     It  is  noteworthy  that  in  all 
these  processes  not  only  is  ionization  present,  but  that  the  ionization 
and  the  nucleation  produced  in  any  definite  process  are  proportional 
quantities.     This  important  result  is  demonstrable  with  phosphorus 
nuclei  by  using  the  condenser  and  electrometer  as  usual  for  the  ioni- 
zation, and  the  steam  jet  for  the  nucleation  ;  or,  with  water  nuclei,  by 
comminuting  water  by  the  aid  of  jets  in  the  fog  chamber,  determining 
the  nucleation  by  the  coronal  method  and  the  ionization  by  discharg- 
ing the  air  laden  with  water  nuclei  through  a  tubular  condenser.     In 
both  these  cases  a  definite  amount  of  nucleation  or  ionization  is  pro- 
ducible, and  may  be  varied  under  control  at  pleasure. 

The  slopes  of  the  lines  in  the  relation  between  the  coulombs  per 
second  passing  radially  in  the  tubular  electrical  condenser  and  the 
liters  per  second  of  air  saturated  with  phosphorus  nuclei  passing  longi- 
tudinally through  the  condenser  into  the  steam  tube,  differ  in  differ- 
ent experiments,  whereas  the  colors  of  the  field  of  the  steam  tube 
referred  to  volumes  of  charged  air  per  minute  are  in  general  agree- 
ment ;  i.  <?.,  whereas  the  nucleation  is  a  fixed  quantity,  the  number  of 
electrons  per  nucleus  varies  with  the  incidentals  of  the  experiment. 
Inasmuch  as  the  ionization  is  subject  to  relatively  very  rapid  decay 
while  the  nucleation  persists,  a  result  of  this  kind  is  to  be  anticipated  ; 
but  detailed  investigations  on  the  rates  at  which  the  ions  and  the 
nuclei  are  severally  produced  in  any  given  process,  and  their  relations, 
seem  to  me  to  be  of  great  importance,  and  are  now  in  progress  at  this 
laboratory, 

110.  Ordinary  dust-free  air  an  aggregate  of  nuclei.— The  steam  jet  * 
shows  that  nuclei  of  small  relative  size,  but,  nevertheless,  large  as 
compared  with  the  molecules  of  air,  must  normally  be  present  in  dust- 
free  air  ;  for  the  axial  colors  may  be  kept  permanent  at  any  stage  by 
fixing  the  supersaturation.      Such   nuclei  may  be  called  colloidal 
molecules,  even  the  largest  being  much  smaller  than  the  ions.    More- 
over, the  available  nuclei  to  be  reckoned  in  millions  per  cubic  centi- 
meter increase  with  enormous  rapidity  with  the  supersaturation  in 

*  Cf.  Barus  :  Bulletin  U.  S.  Weather  Bureau,  No.  12,  1893,  Chapter  III. 


150     NUCLEATION   OF  THE   UNCONTAMINATED   ATMOSPHERE. 

proportion  as  the  molecular  dimensions  are  approached .  But  even 
when  the  yellows  of  the  first  order  vanish,  condensation  probably  still 
takes  place  on  the  colloidal  molecules  specified.  It  is  natural  to  asso- 
ciate these  extremely  fine  nuclei  with  the  existence  of  a  very  pene- 
trating radiation,  known  to  be  present  everywhere.  Moreover,  the 
occurrence  of  many  nuclei  with  but  few  ions  is  not  contradictory,  if 
the  latter  are  only  manifest  when  the  former  are  made  or  broken,  in 
the  manner  suggested  above  (section  89). 

111.  The  nucleation  of  filtered  air.— If  the  filtration  is  moderately 
slow,  and  if  the  pressure  difference,  Sp,  continually  increases,  the 
angular  coronal  diameter  or  its  equivalent,  s,  terminates  in  a  horizon- 
tal asymptote,  as  shown,  for  instance,  in  Chapter  III,  figure  45  et  seq. 
Hence  the  number  of  efficient  nuclei  in  the  exhausted  receiver  eventu- 
ally approaches  a  constant,  specific  for  the  given  rate  of  filtration. 
It  is  probable,  therefore,  that  extremely  small  nuclei  or  colloidal  mole- 
cules (very  small  even  when  compared  with  ions)  pass  through  the 
filter ;  for  in  such  a  case  more  nuclei  would  enter  the  fog  chamber 
during  the  influx  of  filtered  air  to  replace  that  removed  by  exhaustion , 
in  proportion  as  this  exhaustion  (Bp)  is  higher.  Hence  s  should  be 
constant  in  the  manner  actually  observed.  The  study  of  the  succes- 
sive groups  of  nuclei  in  a  scale  of  decreasing  smallness  promises  to  be 
interesting. 

If  the  current  of  air  through  the  filter  is  successively  decreased  until 
its  velocity  all  but  vanishes,  the  asymptote  in  question  may  be  raised 
enormously  until  the  curve  runs  upward  with  a  nearly  straight  sweep. 
Thus,  for  extremely  slow  influx  of  filtered  air  to  restore  the  normal 
pressure  after  exhaustion ,  values  like  the  following  appear  : 

5^  =  24  30          33  37         41 

s  =  rain          5.4        5.8        7.2        7.3 
JV  X  io~3  =  i  105        143        280       351 

data  which,  from  the  nature  of  the  work,  are  inevitably  somewhat  irreg- 
ular, but  which  do  not  even  suggest  an  asymptote,  and  from  which 
the  character  of  figure  46  has  departed.  These  nuclei  can  not  come 
through  the  filter,  for  which  case  s= const,  would  be  conditional.  The 
fact  may  also  be  proved  by  making  observation  but  once  in  24  or  48 
hours,  in  which  interval  all  nuclei  originally  present  would  vanish  by 
time  loss,  unless  constantly  reestablished  as  a  case  of  molecular  equi- 
librium, as  already  suggested.  It  is  possible  to  filter  slowly  enough 
that,  cat.  par.,  a  specific  nucleation  may  appear  for  each  pressure 
difference. 

Experiments  have  been  in  progress  in  this  laboratory  since  May  9, 
in  which  the  nucleation  of  filtered  air  is  examined  daily  with  regard  to 


NUCIvEATlON   OF  AIR,   FILTERED  AND  NOT  FILTERED.       151 

its  time  variation.  To  guard  against  errors  of  interpretation,  it  was 
necessary  to  install  two  fog  chambers  side  by  side,  drawing  from  the 
same  filter  and  utilizing  the  same  exhaustion  system.  In  spite  of 
the  fact  that  all  appurtenances  are  apparently  identical,  the  two 
chambers  do  not  show  even  approximately  the  same  coronas  or  the 
same  nucleation.  Each  behaves  as  if  it  had  its  own  specific  coefficient 
of  radio-activity.  Furthermore,  the  coronas  for  the  same  high  press- 
ure difference  (8 p—^i. 5)  vary  in  the  lapse  of  time  as  if  some  external 
radiation  were  involved,  though  such  a  conclusion  would  not  as  yet  be 
trustworthy.  It  was  shown  above  that  the  efficiency  of  the  very  pene- 
trating gamma  rays  in  producing  nuclei  is  very  marked,  but  the  nuclei 
here  in  question  are  very  small  in  comparison  with  the  cases  examined. 

112.  Nucleation  of  atmospheric  air,  not  filtered— Dust  contents  at 
Providence,  R.  I. — In  the  belief  that  a  highly  nucleated  medium,  no 
matter  whence  the  nuclei  may  arise,  is  a  medium  of  special  interest , 
measurements  of  atmospheric  nucleation  have  been  in  progress  at  this 
laboratory  since  1902.  Four  or  more  observations  were  usually  made 
by  the  coronal  method  per  day,  the  details  of  which  can  not,  however, 
here  be  instanced.*  If  the  mean  of  the  daily  observations  be  taken, 
they  make  up  a  number  of  cotemporaneous  series,  the  properties  of 
which  are  best  shown  graphically.  Apart  from  details,  for  which 
there  is  no  place  here,  the  things  noticeable  in  the  curves  of  successive 
years  are  the  extremely  high  winter,  as  compared  with  the  summer 
nucleations,  the  efficiency  of  rain  in  depressing  the  nucleations,  and 
the  totally  different  character  of  the  curves  for  1902-3  and  1903-4. 

These  may  be  made  even  clearer  by  comparing  the  average  monthly 
nucleations,  as  are  shown  by  the  graphs  in  figure  103  of  Chapter  V,  in 
which  the  ordinates  are  again  the  nucleations  in  thousands  per  cubic 
centimeter.  (Cf.  figs.  102,  104.)  Here  the  degree  of  difference  and 
the  similarities  of  the  two  curves  are  strongly  brought  out.  As  to  the 
latter,  both  tend  to  show  sharp  maxima  near  the  time  of  the  winter 
solstice,  and  flat  minima,  much  subject  to  rain,  at  about  the  time  of 
the  summer  solstice.  It  is  clear  from  the  enormous  difference  of 
nucleation  at  the  maximum  and  at  the  minimum  that  astronomical 
causes  can  not  be  directly  involved.  The  origin  of  the  nucleation 
must  be  in  large  part  local,  the  nuclei  themselves  being  the  initially 
ionized  products  of  combustion.  Nucleation  is  depressed  by  rain,  and 
possibly  also  (from  the  length  of  the  summer  day  as  compared  with 
the  winter  day)  by  light  pressure. 

*  Cf.  Smithsonian  Contributions,  Vol.  XXXIV,  1905. 


152     NUCLEATION   OF  THE  UNCONTAMINATED  ATMOSPHERE. 

113.  Continued— Dust  contents  of  atmosphere  at  Providence  and  at 
Block  Island,  R.  I.,  compared. — To  interpret  the  curves  in  question 
fully,  i.  e.,  to  ascertain  whether  there  may  not,  after  all,  be  a  cosmical 
effect,  superimposed  on  the  local  effect  observed,  it  is  necessary  to 
make  a  series  of  observations  at  a  station  more  remote  from  the  habi- 
tations of  man.  Measurements  were  therefore  made  at  Block  Island, 
under  my  direction,  by  Mr.  R.  Pierce,  jr.,  simultaneously  with  my  own 
observations  at  Providence,  by  the  identical  coronal  method  in  ques- 
tion. The  stations  are  sufficiently  close  together  to  have  nearly  the 
same  meteorological  elements  as  to  wind  and  weather,  but  Block 
Island  lies  well  out  at  sea,  and  is,  in  the  winter  at  least,  nearly  free 
from  local  effect. 

The  average  daily  nucleations  for  both  stations  are  shown  in  figure 
102,  Chapter  V,  and,  as  was  to  be  anticipated,  those  at  Providence  are 
much  in  excess.  Leaving  these  for  discussion  elsewhere,  sufficient 
may  be  learned  from  the  average  monthly  nucleations  in  the  two 
places,  given  in  figure  104,  Chapter  V. 

In  both  cases  there  was  an  evident  tendency  in  1904-5  to  reproduce 
the  curves  of  1902-3  and  1903-4,  with  the  sharp  maxima  in  Decem- 
ber, and  thereafter  a  rapid  march  toward  the  flat  summer  minimum. 
In  both  cases,  however,  there  is  a  new  effect  in  February,  which,  by 
being  superimposed  on  the  local  nucleations  at  Providence,  does  not 
appear  further  than  as  a  determined  departure  from  the  curves  of  the 
preceding  years,  but  which  juts  out  into  striking  prominence  in  the 
observations  at  Block  Island,  where  the  local  effect  is  relatively  negli- 
gible. Apart  from  quantity,  the  fluctuations  of  both  curves  are  iden- 
tical in  character. 

Finally,  as  to  causes  of  the  usual  solstitial  maximum  and  minimum, 
and  of  the  accessory  maximum  in  February  of  this  year,  they  may 
represent  the  diluted  local  effects  averaged  by  the  sweep  of  the  winds 
for  an  enormous  extent  of  territory.  But  it  is  quite  as  reasonable  to 
keep  one's  mind  open  to  the  possibility  that  the  February  maximum, 
at  least,  may  represent  an  external  invasion  of  the  atmosphere  on  the 
part  of  some  external  nuclei-producing  agency. 


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Barus,  C. 

The  nucleatton  of  the 
uncontaminated  atmosphere 


QC918 
B39 


PHYSICAL 
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LIBRARY 

UNIVERSITY  OF  CALIFORNIA 
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Baurs,  C. 

The  nucleation  of  the 
uncontaminated  atmosphere 


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